PC Problem...

[Killa-Eyez]

I've got an old PC from around, uuhm let's say now, 2001?
It's a 1 Ghz AMD Athlon system with an A-bit KT7A mobo.
It has 3 modules of 256 MB Ram in it and an ATI Radeon 7000 VGA.
Also containing a Creative Soundblaster 16 bit sound card, a Realtek RTL8139 Family PCI ethernetcard, a Maxtor HD of 40 GB and 1 of 300 GB.

So here's the deal.
I push the power button, the power led burns, the hd led stays out, nothing happens.
After a couple of minutes I press the reset button and it reboots with both the power and hd led burning only making a cracking noise, kinda like those old harddrives do.
In the beginning of the boot, the cracking starts real loud and rapid.
After a couple of minutes the tempo slows down, and eventually it'll boot showing the Microsoft logo (WinXP MCE) and then make a crack noise and reboot again. This will go on for about an half hour before the system somehow stabilizes ( ) and stays on for a unkown amount of time before it repeats (hoping it doesn't happen while writing this). It also tends to stay on functioning properly for days and only display the problem when I start watching a video.

I thought it is was the harddrive at first but after disconnecting both drives it'd still make the noise. I later found out it was the pc speaker (internal) making the noise, thus concluding (with my usually sufficient knowledge) it's probably an electronical problem.
Now I don't know this, and also doubt if anybody else even heard of such a problem, but please believe when I say it exists, as it's rooting deeper and deeper into my frustration. Knowing a lot of the Gotwoot members know a lot about problems in this area, I humbly await those opinions on this matter as to point out some of the possible causes. Thank you in advance.

I've tried to include as much info possible in this 1st post, but please do not hesitate to ask any.

(PS: My 50th post! Genin! )