Definitely not a virus as I don't do any downloads on that PC - it's strictly a PVR and does nothing but run SageTV (and has for a couple of years with no configuration changes). Firewall is also enabled disallowing all external connections.

The disk is indeed SATA. I did select F6 to load extra drivers and the boot process to recovery was still the same. The last time I did the whole procedure chkdsk actually got 75% of the way through verifying C: and then gave up due to an unrecoverable error.

Because of this I don't believe trying to run through the Windows installation will help - it won't be able to find a previous Windows install if the partition can't be read successfully.

So I removed the disk and connected it externally to another machine. Disk Management sees both the primary and secondary partition and says they're both healthy. Explorer can only read from the second. The first comes up but can't be read.

In a little while I'll try giving it a go with some recovery tools from Acronis to see if I can at least read enough of that partition to rescue my SageTV configuration files. They're all I really want. After that point I won't mind completely reformatting that partition, doing a deep scan for errors and reinstalling plain old XP SP2 fresh. Of course the time-factor is a hassle because I'll also have to reinstall the drivers for the capture card, video card, etc...