I also can't seem to help that much. But first thing I would do is get the HDD out of that computer and connect it as master on the second IDE on a different computer. Then it seems a bit safer to check that HDD. As far as recovery goes, the only program I know is indeed Easy Recovery.
For the problems I also thought at first 'just' a VGA problem - maybe it's getting too hot - but that doesn't seem to explain the HDD problems. Could your powersupply be the problem? Since you get different problems, like RAM, VGA and HDD?
Maxtor has a tool to check the HDD for errors, called powermax. You can download it at the
Maxtor homepage. Don't know how useful it is, though. Good luck!