dj saturn

please help, new here.
ok here we go...
MOBO: asus p5kpl-cm (socket 775 ddr2 4gb max)
cpu: pentium D 960 (3.6ghz dual core)
RAM: 2 x 2gb corsair ddr2 800 OR 2 x 1 gb corsair ddr2 800
video: geforce 9800 gtx+
OS: windowns 7
HDD: sata caviar 300 gb
PSU: 750 Watt Rocketfish

PROBLEM: I just got new ram today, the 2 2gb corsairs and put em in with excitement however, i noticed that i could hear my sata drive spinning loudly which it usually doesnt. The ram worked ok until i did tasks that used up the hdd alot i guess like defragging, copying, it gave me blue screens. So i switched back to my old ram a 2 pair of 1gb corsair and the problem was solved with the HDD causing crashes, but I want my memory upgraded! i ran memtest on the ram and I stopped it at 50% it had no errors so far. im going to run the test overnight but i was hoping for some help before that.

So what i also tried was 1gb stick in first slot and 2gb in second slot for a total of 3 gb and its working out so far no probs.

But when i ran the windows experiance index test thing, it lowered my score by .1 for memory when i had 3 gb opposed to 2 gb of ram.

any suggestions would be appreciated, thanks for reading that long post!