i want to reformat sony viao but it wont read the disk or even external drive. How would i reformat it? It is windows XP.

If you're trying to boot from a Windows CD you need to press F11 as soon as you turn the laptop on. This should bring up a boot device menu. Highlight "CD-ROM" (or the name of your CD drive) with the up/down arrow keys, then press <Enter>.
 
If your cd-rom is already set on the bios priority but still wont read, then the problem might be your windows install disk. try another installer disk, and if the problem is still, then i guess your cd-rom is broken, in that case you have to format your sony viao using a bootable flash drive.
I recommend you to make a bootable flash drive using ISO:
http://www.poweriso.com/tutorials/how-to-make-winxp-bootable-usb-drive.htm


 
Solution
F11 method is not working.. it hangs for a few seconds n then boots up like before... ny suggestions



 
try another installer disk, and if the problem is still, then i guess your cd-rom is broken, in that case you have to format your sony viao using a bootable flash drive.
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