Agree with Nihil and Aspman - check the power supply, provide us with all pertinent data please. Yes, it could be ram, but I'd be more prone to believe the psu isn't strong enough.

Duck - although IDE cabling can fail easily, I sincerely doubt it would be the culprit here - when it fails, you lose the ability to read or write data, or both completely. Least I've never encountered a 'partial ability to read' from one wire broken in the ribbon - the drives always crap out.

Synexic - have you tried BOTH drives by themselves and are they functioning properly when alone in the system? It could also be that one drive itself is crapping out...