Dell Computer Freezes?

A friend gave me a Dell Inspiron 530 and am running a new install Windows XP. The computer keeps freezing randomly. It will run fine for a minute and then freezes but more like a hiccup then a freeze it gets stuck and with some serious lag where you can't do anything. But you can wait it out for a minute and it will run again for a little bit and then freeze again. Sometimes to the point where i have to power down and restart.

Wiped out XP and put Ubuntu I don't have any desire to run Windows. Haven't ran it in ten years not going to start now. A little different but same problems that windows had. Ubuntu seems like it tries to fight the freeze, weird.

So here's what I did:

It has a SATA 1TB hard drive, ran numerous tests on it. All came back negative.

2Gb of ram numerous tests on it all good there too.

512nvidia pci/express ran tests on it( kind of like the ram test) real extensive everything checks out.

Jumped the BIOS to reset it, checked for BIOS updates.

Replaces the cables on the inside. SATA cables, check voltage on power supply. Checked Battery every things Tip Top.

Then I thought what the hell I'll completely clean the whole computer, maybe its some dust somewhere, stripped it all apart like your field cleaning your gun. New thermal compound cleaned fans, it looks brand new again.

So then i started running tests on the processor speed test and stuff like that to get it real hot everyone always says "oh yup your computers getting too hot thats the problem" nope it ain't.

So between fighting the stupid freezing and hiccups and crap like that, I manage to run every test and do everything I can think of to fix it. I'm thinking that maybe the whole motherboard is shot. But where, cause i would really like to know. And is there a extensive motherboard testing program out there, everything i see has to run through windows and most of the utility's i am running to test my CPU are of a Live CD or a Bootable CD or thumb drive. And thats crazy to cause I can run the Utility CDS and Knoppix cd no problem with no hiccups or nothing. So then i think maybe it is the hard drive but can a hard drive come back with no errors but the read head is the one with the error? Enough Rambling! Let me know if you can think of something. Maybe it needs a exorcism! Take it to Church and get it done.