If you can't start it up then I would suggest to simply reformat it. And no you couldn't delete the file in the temp folder. Most of these types of virus are hidden. I followed the path of the virus that the HijackThis gave me and found nothing, yet it was still there. And it could also be in a different folder, these viruses like to hand around in the Win32 folders.
If you can't get into windows then the virus might have deleted the OS files. I had a virus(Massive boot virus) on my old computer with XP SP1 and I left it on for a while. The next time I turned it on, nothing. Went to reformat it, it didn't even detect the windows installation on the HDD. It deleted all my files!
I think you can run the HijackThis off of a boot disk, but i wouldn't go through the trouble. Reformatting takes about an hour at most. Do you have any important files on the computer?
Four years back huh?
Upgrade time, No?
You could always buy another OS Disk.