For some reason, even with my fast-ish PC (Pentium D 840 3.2Ghz 1gb ddr2 ram sata hdd pci-e videocard etc.) my explorer lags a lot. I have a small widget telling me CPU usage, and when surfing or idling it rarely goes above 10 (unless it's scanning files), but a lot of the time I'll have an explorer window open and it'll lag. It freezes the start menu, and the window, sometimes desktop icons sometimes not, but it won't freeze any other programs (sometimes windows media player but it's rare). The CPU usage doesn't get above 15% in this instance, so it can't be that it's maxed out. The HDD shouldn't affect it to my knowledge, but either way the hdd usage light isn't running solid, it blinks indicating normal use, but still I have issues. I constantly clean up my computer, I have all sorts of tweaks and I disabled a bunch of unnecessary services, but it's happened before I even started to tweak. I understood when it happened when browsing my IDE hard drive, but not the SATA.

Any clues?

Also, sometimes when launching EXE's, no matter the size or how CPU intensive they are, it does the same thing.

To me it sounds like the hard drives are struggling...have you ran chkdsk /f on them? defragged them recently? (don't mean to be condescending, just if i dont ask i won't know).

I've chkdsk'ed 2 or 3 weeks ago, and I defrag every 5 days.