that's weird because you first wrote you have two "primary IDE channel"
anyway so you must have two connectors on the mobo and just one cable ? and you have it connected to the second IDE connector which is "secondary IDE channel" -that's logic and in this case you have proper ultra DMA mode (5 probably)
although it's recommended to have DVD on separate channel/cable (and the HD on the end of the cable as 'master' if on the same cable with DVD) it would not be a reason as you didn;t change this and it was working fine for 2 days as you mentioned
You can do some HD diagnostics additionally but as you didn;t change the HD also it's less likely
If you changed the mobo and CPU to much more power demanding and didn;t change the PSU at the same time it's the most likely reason and most dangerous to the whole system! (it may get worse and damage mobo/cpu and the rest!)
You should measure the voltages by a hardware gauge/measurer but as you probably can't do so you'd better quickly run for a BRANDED PSU (corsair or sth) with at least 450W on it !!
otherwise you risk exposing yourself to a longer break in Wow
LOL
i'm leaving work so I'll pop in later