Ctrl+F11 won't work - system restore

Hi,

I have a DELL Vostro 200 PC.  My computer is badly infected with viruses.  I was trying to restore the PC by using Ctrl+F11 but the system won't let me get into it.  I  have tried F8 but that option won't let me get into the Advanced boot option either.  The OS I am running is Windows XP Home.  I thought maybe switching the keyboard would help as I am using the USB keyboard.  I was going to use the old legacy keyboards only to discover that the PC doesn't even have that slot.  It only accepts USB interface keyboards.  I need this computer urgently.  Please help and let me know how I can restore the PC to factory default settings.

Also note that I have tried to do a system restore by going into Start--> All Programs -->  Accessories --> Systems Tools -->  System Restore to the first date I purchased this PC.  But that won't work as the computer is badly infected with viruses and won't let me do anything.  Please help!

Thanks.

The keyboard is connected thru a USB adapter.  There is no slot