I said certain hardware...it's either mobo or cpu, as far as i recall.

Yeah, a mobo is where MS draw the line (from what I recall) so an OEM copy of Windows would be tied to that mobo. You can't replace it and keep using OEM Windows and stay within the EULA. You can still use it... just not within the EULA.

All I know is nothing like that ever happened to me. Must be an isolated case, then.
Wouldn't the OEM copy be tied to the BIOS chip in that mobo somehow?

Nah, it's pretty much an honour system. Not that I've put it to the test or anything...

And that's why I chuck out the OEM version of Windows. So I don't have to muck about with an "honor system".

I can't say I had any hassle at all with the last OEM copy I had. It doesn't even need activation. I think they might have removed that given how they completely ballsed up OEM XP activation.

A CPU change alone should never deactivate Windows, not even an OEM copy that is tied to the hardware you installed it on. Even a CPU, GPU, and RAM change isn't enough. But a motherboard or BIOS change usually will.

How you acquired the copy of Windows makes a difference. "SLP" copies of Windows that come preinstalled and preactivated are tied to the BIOS. You can only replace like for like; usually, you may transfer that copy of Windows to another computer from the same manufacturer (or to another motherboard used in the same manufacturer's computers).

OEM and Retail copies of Windows are the ones that use a similarity score. The most important component for similarity is the onboard NIC. Because changing the motherboard necessarily changes the onboard NIC and some other components, it usually pushes the count of differences into deactivation territory.

Bulk License copies of Windows don't use this activation mechanism at all. XP allowed any non-blacklisted product key. Vista and W7 use activation servers that charge the activation against the owner of the bulk license.

If I may add to cjrgreen's comment:

This does not mean you necessarily need to buy a new XP disk or license should the Genuine whatever system kick off and tell you your copy won't work at install.

In my experience, Microsoft customer service is pretty decent when it comes to activation. I call them, explain I replaced a failing part (last time it was my mobo and CPU), give them my original key, and a little while later, they give me a new key... and I finish my installation.

I have a ~10 yr old retail disk and have done this numerous times for re-installs, rebuilds, and repairs. The 20 min phone call is by far the least annoying part of the re-install (downloading 10 years of service packs and updates... sigh).

My mistake. Nor for windows XP at leasr. Changing the CPU alone will not invalidate the licence but may trigger a wrong WPA calculation ( WPA is an index calculated by windows to check if the OS is installed on the right machine ) and have to re-activate the licence with MS.

Other OEM software might be subject to mre restrictive policies.

Ok thanks for the information. I’m going to just upgrade the RAM, give the PC a good cleaning and put new thermo grease on the processor for now.

I got the 2GB RAM today. I installed it into the computer but when I turn the PC on I get no video output/ maybe not starting up at all. Is there anything I need to do before I install the RAM? Could it be a compatibility issue?

Yes, it's a compatibility issue. You were misled, that RAM is not compatible with your computer, and nothing you can do will ever make it compatible with your computer. Flog it on eBay or give it to Goodwill, and put your old memory back. Then go back to Navagon's post, where he gave you a good link to memory that will actually work in your computer.

This is why posters giving other people advice on what to do with their money should research their claims before they post them, dammit.

No big deal that kind of stuff happens when you’re not really sure what you’re doing. I can return the chip and get my money back. I choose this RAM over the price instead of doing research.

It was an accident. :P :)