Troubleshooting Steps for Windows 7:
Step 1: Done. 1 Trojan detected. Unrelated to the problem.
Step 2: Didn't help.
Step 3: Didn't try, but I think the PC would be consistently slow if it was for a performance drag. It definately wouldn't be a problem after a fresh windows install I did.
Step 4: I don't get any errors, crashes or anything, so no.
Step 5: Attached report. report.zip
Step 6: I haven't been experiencing errors.
Step 7: When the slowdowns occur, none of the programs such as task manager work properly anyway, so it is pointless I guess. The computer "acts" like nothing had happened after the slowdown is over.
Step 8: Tested with memtest overnight. No errors.
Step 9: I don't see how it helps, I just recently formated all but two partitions (two minor, mostly unused partitions) and defragmented them.
Step 10: Doesn't help.
Step 11: Temps are high as it is summer, but nothing unreasonable.
Step 12: The device drivers are always automatically downloaded.
Step 13: Done that.
Step 14: Did a clear reinstall anyway.
Step 15: I'll edit the post and add the results later. EDIT: No integrity violations found.
Step 16, 17: The OS is 2 days old. I don't think there is a need for that.
At last, I don't think it is a PSU issue. My HD 5870 is quite a power hungry card and the slowdowns can occur even if the load on the card is 0%. I don't think it is Adobe Flash as it would've occured since the day I purchased the computer and as it happens even while I am not using anything associated with it.