For the past 2 years or so (4 year old custom build) I've been getting random moments where everything stops responding (or takes a very long time to respond) followed by I/O and hdd not detected errors on restart. To fix it, all I usually need to do is unplug my SATA cables from the hdd and mobo and plug them back in again and the problem disappears, at least for a little while (it ranges anywhere from a day to a few months time). Sometimes even a startup repair does the job. I've done multiple reformats and have also ran chkdsk more times than I can remember and both do not seem to help in the long run. Both the drives seem to be exhibiting the same problem. Have both my hdds been "dying" for the past couple of years, even though they are fully functional besides these occasional hiccups? Does the issue lie elsewhere? All feedback is appreciated.

System specs:

Biostar Tpower i45 mobo

2x WD Caviar 640GB hdds

Zalman 750w psu

Radeon 5870 gpu

2x2gb Gskill DDR2 ram

Win7 64