Hi, guys!
My apologies for coming with such old issues but after reading around and trying a few tricks, I made a bad mistake and now I'm completely at a loss. If anyone here is kind enough to offer a few pointers - be it in a PM if they want to protect their knowledge - I would be extremely grateful.
I'll try to be brief (but I may not succeed): after cleaning a bad virus off of a friend's PC, a week later he called saying computer won't boot anymore. Went over, started it up, it was an extremely slow boot. Powered it off, took it at home and tried to find and fix the issue.
First off I mounted the drive in one of my spare machines and started HDD Regenerator 1.41 in DOS mode as I had done many times before with my own discs. At some point it bailed out, saying something about a SATA controller (none on the board, drive is ATA), so I rebooted and at that point the drive wasn't recognized properly by the BIOS. HDD Regenerator wouldn't detect it anymore, neither would HDAT2.
I went off and bought a new HDD for my friend's machine, installed it, put the OS and everything else, ready to get the files from the old HDD. After finding this place and reading around for hours, I downloaded and ran HDD Repair 2.0. I know, people say it's buggy and whatnot. Thing is, by fortune I managed to bring the drive back to a working state by replacing some of the corrupt modules with ones from an archive found here in the firmware section, from an identical drive.
Upon reboot, the drive was again recognized by the BIOS, MBR, BOOT and TABLE were found upon a HDAT2 scan, I even saw the files and folders in DOS under Volkov Commander with NTFS4DOS, so everything appeared to be just fine. All I had to do was mount the drive in the original machine and copy the files over.
But no, I had to perform one more scan with HDD Regenerator, because one of the bad SA modules had been the G-List and figured there may be true bad sectors on the drive. And indeed they were, about 210 before HDD Reg bailed out again. I rebooted and this time no problems, so ran HDD Reg once more to check the remainder of the drive. It found other bad sectors throught the drive and again it bailed out.
But this time I made a critical mistake: instead of powering off and then back on as stated on the screen, I unplugged the drive's power molex, plugged it back in and restarted HDD Reg. That was stupid, I know now, but you can say it a thousand times - I wouldn't mind. Thing is, right after that a few thousand sectors starting from the first were marked as bad, until I interrupted the scan.
Expectedly, upon reboot the drive was again improperly recognized by BIOS. Tried to restore it again through HDD Repair 2.0 using the same loader as the first time. This time other modules were corrupted, including 0008, which is labeled DISK and 4532 (or similar). I overwrote module 0008 with the one from the archive unaware that the serial number was in there and it obviously way different. Dunno if it matters though, but later on I changed it to the original serial number as found on the drive's sticker. I also tried to restore 4532, which is all zeroes in the archived copy.
Thing is, the 4532 module only apparently gets repaired, because on subsequent checks it keeps throwing an error. Therefore I suspect the respective sector (module is one sector long) is damaged on the drive. Reboot will keep showing the drive as badly recognized in BIOS, HDAT2 reports 'firmware corrupted' and 'DCO frozen' so it can't repair or unmark sectors previously marked as bad by HDD Reg (although I overwrote the G-List again with the empty one from the archive). I suspect a relocation but I have no idea how to check (and restore).
So basically the problem appears to be: firmware is corrupted by possible/apparent bad sectors and access to repairing is locked through DCO or whatever. Seems like a deadlock but I really wish theire is still hope. I really need to get as much data back from the drive as possible, because there's family photos in there and others of sentimental value. And just in case you'd be inclined to refer me to professional data recovery services or say "it's toast, nothing can be done", please don't, because I cannot afford the former and cannot accept the latter.

If anyone has the good heart to offer a few valuable hints, please do speak up. I'm really at wit's end and my friend is eagerly waiting for good news from me, while I'm overwhelmed with shame for my sheer stupidity. Thank you and apologies for not being as brief as I wanted to.