hello, little help plz?

Greetings, I am having some computer issues perhaps some of you would kindly help me solve my problem. About one week ago i turned on my computer and received a cpu fan speed warning, i looked in the case and it wasn't spinning at all. so i took it to my garage and blew a ton of dust out of it.
Then everything seemed to work normally. until about 2 days ago my PC was running fine for a few hours then it started lagging hard, it was playing music and seemed to skip and play half a second of music then pause and another half a second, etc. i couldn't shutdown from within windows, so i turned it off with the front power button. now i can turn it on and it will go through POST and i am able to log onto windows and get to the desktop but right when i log on i get the hour glass and nothing will load it stays like that for ever. I can move the mouse and click on the start menu but other then that nothing will launch.

And it wont go into safe mode at all. every time i try to boot to safe mode it shows all that scrolling white text garbage but then just resets and goes right back to 'how do you want to start windows : normally, safe mode/with CMD/with networking, last know good config, etc.'

but no matter what i choose it just goes back to that screen.

I am able to access the bios and they show that the CPU fan is running fine: 4000+ rpm and idleing at 33 degrees celcius. and the 'core temp' is 29 degrees celcius and the chipset fan is spinning fine also.

I have tested my memoryswapping 1 stick at a time and that doesnt fix the problem. also i tested the with bootable memory diagnotics no problems with that.

i have tested my power supply connector with a multimeter all the voltages seem to be correct at around 12, 5, or 3 or -12, -5, -3 volts. the only thing is on the ATX main motherboard power connector i get a reading of about -4.5volts of pin 20 (white wire) I think its supposed to be -5 volts right? but also it says pin 20 might not be used so i don't know.

I am thinking maybe my motherboard or cpu has a problem

oh i also tried swapping my IDE cables on my harddrive so i dont think its a HD problem.

over all i think i narrowed it to my MoBo, CPU or maybe my Powersupply.
also maybe its just a virus? lol what do u think? i dont wanna reformat windows and lose a lot of important files.

can any of u help me out here i would really appriciate it. really!

Thanks in advance!


Oh yeah.

It a custom built:

AMD athlon 3500+ with a replaced (upgraded) cooling fan
1 gig crucial ddr memory
430 watt thearmaltake powersupply
Asus MoBo with nforce 4 and AMD socket 939 CPU slot
80 GB maxtor IDE Harddrive

 

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