Check the label on the power supply. 300w and you're in good shape for your config. If the power supply is only 250 w that could be a problem.
I haven't really seen power supply problems cause HDs to act badly but I learned to never rule out anything when a PC gets flaky.
Does the case have enough cooling (more than just the power supply fan) to get the heat out? Check your MB temperature (BIOS, Sandra, Gigabyte utility) it should be 35-45 deg C, preferably the low end. Or stick a thermometer in the case and run for a while, then pop the lid and check the temp.
Run the WD utility (download it from the
www.westerndigital.com ) to see if the drive has a health problem, it fits on a floppy. Remember WD has a 3 year warantee and RMA is a peice of cake if their health check utility says the drive is flaky.
The MB runs a health check every time you boot and if a problem crops up it should report it.
Sisift Sandra has a suite of burn in tests, but be careful they can fry a system. Better to run the WD stuff first in case it reports a failure, print it and do the RMA route.