Windows 7 hangs for a few minutes

Hello!
My specs, first of all: Asus P5B (P-965 series), Intel Core 2 Duo e6600, 2 Seagate 160GB HDs, 1 WD 500GB (ALL SATAs), Sony NEC Optiarc 24x SATA writer, 2x1GB Kingston and 1x1GB Transcend DDR-2@667MHz, nVidia GeForce 7300GS.
I am running Windows 7 RC1 and it's a Clean Install.
I was experiencing this problem before as well, but it seemed to have gone away for a short while. But When I put in my new WD 500GB drive, it seems to have come back. Although I can swear there is nothing wrong with the HD, since the problem was there before as well.
When I'm in Windows, say listening to a song or something, the rest of the computer would freeze/hang RANDOMLY for upto 5 minutes :/ I mean, the song would still continue playing, but I can't do pretty much else. The mouse moves and even Ctrl-Alt-Del doesn't work. VERY annoying. I either have to wait for 5 minutes, after which the computer runs pretty slow and hangs again after sometime, or force restart.
I've done EVERYTHING possible: Flashed BIOS, reset CMOS, switched around the SATA ports for my different devices, reinstalled Windows at LEAST a million times.
I thought it was an overheating problem (and sure enough, my HDs DO run pretty hot to the touch; ie, I can't even touch them without wincing). Even my CPU was running at 73C (O.o). So I cleaned everything inside and now it runs at 53C, constant.(Doesn't exceed 60, whatsoever).
I am on the verge of tears. Please tell me what to try next?
Is it really an overheating problem? I mean can overheating lead to hangs of the kind I've described? Also, my BIOS is on pretty much its default settings: non-AHCI, ACPI enabled, etc etc.
Another peculiar thing: Sometimes, my BIOS takes AGES to identify my HDs. Like even upto a minute :/ And at times, it's instantaneous.
VERY weird, ehh?

I have a 450W power supply, btw.

Hi muth56 and welcome to W7 Forums!

It does sound like this could be a drive problem, I would suggest running a drive fitness test to try and rule it out. If you download the Ultimate Boot CD (http://www.ultimatebootcd.com/) and burn it to a CD (or USB stick if you want), then try booting the computer from that. You'll be presented with the official tools for almost all drive makes, which will scan and list any problems with your drive.

53C is a much healthier temperature for your CPU What is your PC cooling like overall?

Hi Ian! And thanks for the reply!
However, I DID run the SeaTools utility and scanned each and every hard disk. There doesn't seem to be a problem with the disks, so that can be ruled out :/

There might be something wrong in the BIOS settings, though. Do I need to change something? (PIO, DMA, etc).
Also, I have two different brands of DIMMs. Can that be a problem?

Was that run using the full drive test? It seems odd that your mothboard can take up to a minute to detect the drives, does it do this when you use each as a single drive in your system?

You can try searching for a BIOS update and apply that, which will also reset the settings back to defaults which should work.

Is your memory the exact same spec (same timings etc...?). It's not ideal, but as long as the specs are the same it should still work. I would try taking leaving in one of the pairs and see if that helps things. FWIW, you can test your memory using http://www.memtest.org/