[Zoolander]

If you want to go all out and really find if it's your PSU,

Here is how I have approached the initial design of an industrial PSU. I work as a co-op doing electrical and computer engineering, and I have never heard of a "dying PSU", but I have heard of a strained PSU.
One of the things that electical engineers typically would do is this to determine if they have enough power from their supply (on each line ie: the 3.3v, 5v, 2.5v), is find all the typical/maximum current's for each device as well as any internal typical/maximum currents for each device. Meaning if you could find out the typical/maximum currents for your mobo/pump/HDD/DVD/CD and see if it exceeds what your power produced by your PSU. This can be determined from the simple eq: P = IV (V being probably 5 volts) Since everything interfaces at the same voltage I'm guessing, that one of your 5volt supply is droping your power low. To test this you could test your 5 volt line while the system is running the benchmarks. Although, this might be too much work.

Davis