al seleccionar un radio button se borran los selec option

[Ariel1986]

cuando selecciono un radio button se me borran todos los option select del formulario

<form action='' method='post' name='formulario'>
<div align='center'>
<br><IMG src='IMG/barrahc.jpg'><br><br>
<font face='arial' face='2' color='#026CB4'><b>Folio</b></font>
<font face='arial' face='2' color='#026CB4'><b>: </b></font>
<input type='text' name='folio' style='color:#0260A2' >

<font face='arial' face='2' color='#026CB4'><b>Fecha</b></font>
<font face='arial' face='2' color='#026CB4'><b>: </b></font>
<input type='text' name='fecha' style='color:#0260A2' onBlur='valido()'><br>

<br><IMG src='IMG/barrahc.jpg'><br><br>

<font face='arial' face='2' color='#026CB4'><b>Datos del cliente</b></font><br><br>

</div>

<table border="0" align="center" >

<tr>
<td><font face='arial' face='2' color='#026CB4'><b>Rut</b></font></td>
<td><font face='arial' face='2' color='#026CB4'><b>:</b></font></td>
<td><input type='text' name='rut' style='color:#0260A2;' onBlur='valido()'></td>
</tr>
<tr>
<td><font face='arial' face='2' color='#026CB4'><b>Telefono</b></font></td>
<td><font face='arial' face='2' color='#026CB4'><b>:</b></font></td>
<td><input type='text' name='telefono' style='color:#0260A2;' onBlur='valido()'></td>
</tr>

<tr>
<td><font face='arial' face='2' color='#026CB4'><b>Ciudad</b></font></td>
<td><font face='arial' face='2' color='#026CB4'><b>:</b></font></td>
<td><select name='ciud' style="display:block">
<option value='Temuco' style='color:#0260A2'><b>Temuco</b>

</select></td>
</tr>
</table>

<div align='center'><br><IMG src='IMG/barrahc.jpg'><br><br>
<font face='arial' face='2' color='#026CB4'><b> Datos de atencion</b></font><br><br>

<font face='arial' face='2' color='#026CB4'><b>Atendido por</b></font>
<font face='arial' face='2' color='#026CB4'><b>:</b></font>
<input type='text' name='atendidopor' style='color:#0260A2;'

onBlur='valido()'>&nbsp&nbsp&nbsp


<div align="center"><br><IMG src='IMG/barrahcor.jpg'>
<p><font face='arial' face='2' color='#026CB4'><b>Tipo de Equipo</b></font></p>
</div>
<p align="center">
<input type="radio" name="rad"

onClick="activar('marcap','disco','memoriap','tarv ideo','tarsonido','tarred')"/>
<font face='arial' face='2' color='#026CB4'><b>Computador </b></font>
<input type="radio" name="rad" onClick="activar('marcai','modeloi')" />
<font face='arial' face='2' color='#026CB4'><b>Impresora </b></font>
<input type="radio" name="rad" onClick="activar('red')" />
<font face='arial' face='2' color='#026CB4'><b>Red</b></font> </p>
<tr>
<p align="center">&nbsp;</p>
<table width="75%" border="0" align="center">
<tr>
<td width="262" height="28" valign="top"><font face='arial' face='2'

color='#026CB4'><b>Marca:</b></font>
<select name="marcap" style="display:none">
<option>AMD</option>Marca
<option>Packard Bell</option>
<option>Olidata</option>
<option>Intel</option>
</select></td>
<td width="156" valign="top"><font face='arial' face='2' color='#026CB4'><b>Marca:

</b></font>
<select name="marcai" onChange="cambiar()" style="display:none">
<option value="brother" selected>Brother</option>
<option value="canon">Canon</option>

</select></td>
<td width="148" valign="top"><font face='arial' face='2' color='#026CB4'><b>Tipo:

</b></font>
<select name="red" size="1" style="display:none">
<option>Electrica</option>
<option>Telefonica</option>
<option>Datos</option>
</select></td>
</tr>
<tr>
<td height="28" valign="top"><font face='arial' face='2' color='#026CB4'><b>Disco:

</b></font>
<select name="disco" style="display:none">
<option>10 GB</option>
<option>15 GB</option>
<option>20 GB</option>
<option>30 GB</option>
<option>40 GB</option>
<option>60 GB</option>
<option>80 GB</option>
<option>120 GB</option>
<option>mas... GB</option>
</select></td>
<td valign="top"><font face='arial' face='2' color='#026CB4'><b>Modelo: </b></font>
<select name="modeloi" style="display:none">
<option value="HL-1230" selected>HL-1230</option>
<option value="HL-1240">HL-1240</option>
<option value="HL-1250">HL-1250</option>
</select></td>
<td valign="top"></td>
</tr>
<tr>
<td height="31" valign="top"><font face='arial' face='2' color='#026CB4'><b>Memoria Ram:

</b></font>
<select name="memoriap" style="display:none">
<option>64 Mb</option>
<option>128 Mb</option>
<option>256 Mb</option>
<option>512 Mb</option>
<option>1 GB</option>
</select></td>
<td valign="top"></td>
<td valign="top"></td>
</tr>
<tr>
<td height="28" valign="top"><font face='arial' face='2' color='#026CB4'><b>Tarjeta de

Video: </b></font>
<select name="tarvideo" style="display:none">
<option>Integrada</option>
<option>si</option>
<option>no</option>
</select></td>
<td valign="top"></td>
<td valign="top"></td>
</tr>
<tr>
<td height="28" valign="top"><font face='arial' face='2' color='#026CB4'><b>Tarjeta de

Sonido: </b></font>
<select name="tarsonido" style="display:none">
<option>Integrada</option>
<option>Si</option>
<option>No</option>
</select></td>
<td valign="top"></td>
<td valign="top"></td>
</tr>
<tr>
<td height="28" valign="top"><font face='arial' face='2' color='#026CB4'><b>Tarjeta de Red:

</b></font>
<select name="tarred" style="display:none">
<option>Integrada</option>
<option>Si</option>
<option>No</option>
</select></td>
<td valign="top"></td>
<td valign="top"></td>
</tr>
</table>

<br><IMG src='IMG/barrahcor.jpg'><br><br>



<font face='arial' face='2' color='#026CB4'><b>Nº serie</b></font></td>
<font face='arial' face='2' color='#026CB4'><b>:</b></font></td>
<input type='text' name='serie' style='color:#0260A2'

onBlur='valido()'>&nbsp&nbsp&nbsp


<br><br>
<font face='arial' face='2' color='#026CB4'><b>Informe de atencion</b></font>
<font face='arial' face='2' color='#026CB4'>:</font><br>

<textarea name='informe' cols='70' rows='5' ></textarea>
<br>


<br><font face='arial' face='2' color='#026CB4'><b>Traslado</b></font>
<font face='arial' face='2' color='#026CB4'><b>:</b></font>
<select name='traslado'>
<option value='Si' style='color:#0260A2;'><b>Si</b>
<option value='No' style='color:#0260A2;'>No
</select><br> <br>

<font face='arial' face='2' color='#026CB4'><b>Reparación</b></font>
<font face='arial' face='2' color='#026CB4'>:</font><br>

<textarea name='adicional' cols='70' rows='5' ></textarea>
<br>
<div align='center'><br><IMG src='IMG/barrahc.jpg'></div><br>
<font face='arial' face='2' color='#026CB4'><b> Valores</b></font><br><br>

<font face='arial' face='2' color='#026CB4'><b>Valor</b></font>
<font face='arial' face='2' color='#026CB4'><b>:</b></font>
<input type='text' name='valor' style='color:#0260A2'

onBlur='valido()'>&nbsp&nbsp&nbsp

<font face='arial' face='2' color='#026CB4'><b>fecha pago</b></font>
<font face='arial' face='2' color='#026CB4'><b>:</b></font>
<input type='text' name='fechap' style='color:#0260A2'

onBlur='valido()'>&nbsp&nbsp&nbsp

<br><br><font face='arial' face='2' color='#026CB4'><b>Pagado</b></font>
<font face='arial' face='2' color='#026CB4'><b>:</b></font>
<select name='pagado'>
<option value='Si' style='color:#0260A2;'><b>Si</b>
<option value='No' style='color:#0260A2;'>No
</select><br><br>

<input type="radio" name="tipadoc" onClick="activar('factura')"/>
<font face='arial' face='2' color='#026CB4'><b>Nº Factura </b></font>
<input type="radio" name="tipadoc" onClick="activar('boleta')" />
<font face='arial' face='2' color='#026CB4'><b>Nº Boleta </b></font>
<br>
<select name="factura" onChange="cambiar()" style="display:none">
<option value="0001" selected>0001</option>

</select>

<select name="boleta" onChange="cambiar()" style="display:none">
<option value="0001" selected>0001</option>
<option value="0002">0002</option>
<option value="0003">0003</option>

</select>




<div align='center'><br><IMG src='IMG/barrahc.jpg'></div><br>
</div>


<center>
<input type='submit' name='enviar' value='Agregar Registro' style='background-color:

#0466AA;color:white'>
</form>