EDIT: I JUST NOTICED THE NOISE SOUNDS LIKE A CD NOT SPINNING PROPERLY, LIKE WHEN YOU PUT A COMPUTER GAME INTO A PS2 EXCEPT THIS IS COMING FROM THE BACK. IT SOUNDS SORT OF SCRATCHED IF YOU KNOW WHAT I MEAN.

Ok, here's the problem. A couple of days ago, my computer started making these really strange, loud noises. The sound was obviously the sound of a fan spinning really loud, and abnormally. I got scared, so I immediately hit the shut down button. I turned in on again and there was the sound again, but not as loud, then 10 seconds later, it got loud again! I shut down. This time,  I waited 5 minutes. Then I turned it on, ignoring the problem. But I shouldn't have, because the next day it happened again. This time, when I restarted, I got the so called 'blue screen of death', this is what it said:

A problem has been detected and windows has been shut down to prevent damage to your computer.
BAD_POOL_CALLER

DISABLE BIOS memory options like caching or shadowing.

Beginning dump of physical memory.
Physical memory dump complete.

STOP: 0x000000C2 (0x00000043,0xD68C0000, 0x00000000, 0x00000000)

And it told me to restart in safe mode to disable caching/shadowing and contact a comp tech team. I tried to restart in Safe Mode but I got it again everytime, including all other modes, like Start Windows In Last Known Good Config (something like that).

So I reformatted my computer, losing everything. After reinstalling everything, I thought the problem was gone, phew! But I was wrong, the sound came again and I was forced to shut down. When I restarted this time, I got the message (with the blue screen of death):

DRIVER_IRQL_NOT_LESS_OR_EQUAL

MpFirewall.sys - Address EF8A2257 base at EF89A000, Datestamp 43025830

and then that Physical Memory dump again...

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What is the problem?

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And, another thing I NEED help with. Computer lag. I just reformatted my computer, but everything is lagging, not as in slow, but when I scroll up and down in a net browser, it moves in waves. This also HAPPENS when I try to move a program window around, it goes really slowly, smooth scrolling doesn't help. Help please?

I use a Dell Pentium 4, 1gb RAM, 250GB Hard Drive (which I REPLACED the 80gb with). This computer is just over 1 and a half years old.

Thanks.
Also, when I'm scrolling on a browser, the cursor lags like *censored* as well.I would open the case and identify WHERE the sound is coming from. It may be a bad or clogged fan, a hard drive, etc.

Free RAM test download at www.memtest86.com

Free hard drive diagnostic download at the appropriate drive maker's site.

Let us know about the sound origin and the above.