Complete Crash Through Antivirus Malware

The computer is a fairly ancient HP ATI Radeon 9000 desktop, with 2.53GHz Intel Pentium 4 processor, 256 DDR SDRAM, 60GB hard disk, Windows XP Home Edition (SP3) and HP Pavillion 150s flat screen monitor.
I clicked on a link in an email, and a file started downloading and installing itself (no option to 'cancel').
A minute later a lot of windows with warning and error messages etc popped up, all telling me that the computer had been infected by a virus and offering antivirus software for the removal of the virus. I kept closing the windows as this was evidently a case of malware, and tried the following:
- I tried to find and remove the installation through Add/Remove Programs, but access was blocked
- I tried to do a System Restore, but got a message that the Administrator had disabled this option (not true) and that I needed Administrator Rights to change the settings (I have administrator rights)
- I tried a restart in Safe Mode, but it refused to do so (hanging at roughly the half way stage)
- I then tried to restart again, several times, but startup now didn't even get me to the halfway stage; in fact the computer does not even respond now to any of the 'F' keys at startup, i.e. I can't even open the System Page (to use the 'Safe Mode' option etc); all I get now at startup is the HP logo (for a few seconds, followed by a blank screen)
- someone gave me a bootable 'Recovery Disk' to put in the CD drive, but the computer does not open the program (blank monitor)
- the same is true for the bootable Windows XP Home Edition Installation disk (monitor goes blank)
- and the same is true when I put a bootable disk with DIBAN (Darik's Boot and Nuke) hard disk wipe / reformatting utility in the drive (blank screen only).
I couldn't find such an extreme case documented anywhere in this forum, hence a new thread.
Any help would be greatly appreciated as I can't afford a new computer and I urgently need to complete my thesis.
Thanks!

 

Thanks for all the advice!
As to 'taking the hard disk out': I assume you mean physically removing the hard disk from the HP, then putting it into another desktop as a secondary hard disk and scan it from that computer's primary hard disk? The problem is that I don't have easy access to another desktop (my friends have all laptops). Or can a desktop's hard disk somehow be attached to - and scanned from - a laptop?
As to your other questions: my crashed desktop does NOT respond to any 'F' keys at startup, i.e. can NOT be booted into BIOS; it is set to boot from CDs, but when I place (what I believe are bootable) CDs in the CD drive and then start the computer (see my original post) it doesn't boot from the (bootable) CDs - all that happens is that the HP logo appears for a few seconds and the CD drive becomes active (some whirring noise, its light flashes for a few seconds or so), then the screen turns blank.