Why does my Vista sometimes think it's not legit?

I have an intermittent problem on my computer: every now and then Windows seems to think it’s been altered and is no longer a legitimate copy. I get the popup with the red stopsign with the X in it saying “Windows has determined it’s been altered. Find out more about Windows, blah, blah, blah.” Your choices are “learn more” and “close.” Hitting “Learn More” takes you to a web page that talks about Gen-U-Ine windows. Hitting “Close” exits you out of Windows.

This will happen (rarely - maybe once or twice a month) when I’m just sitting at my computer - there’s no apparent pattern to what I’m doing - I might be browsing, I might be just sitting there. It also happens when I reboot my computer (maybe one out of every 5 reboots) and more frequently when my computer restarts after a power outage (about half the time). I’m usually able to make it to go away by rebooting into safe mode, then booting into regular mode. Sometimes I have to do this a couple of times before Windows regains its sanity.

However, I’m worried that someday I won’t be able to make it go away and I’ll be screwed. I know this is an authentic copy of Vista, as I built this machine with hard and software purchased from Newegg, and installed it myself. Of course I have the install disc sitting on my shelf.

When I read about this problem, the explanation and solution for the problem always seems to be on the order of “something you installed corrupted a windows file, go to a restore point, go to a backup, etc.” - but I haven’t installed anything outside of a game or two in the past months (maybe some games through Steam, Witcher2, not much else). Plus, I can go for a really long time with no problems.

I’m running virus checkers, Windows Defender, have a firewall going, etc, so I don’t believe that is a factor.

So the question I have is this: is there some sort of preventive action I can take to make this problem go away? I suppose I could backup my files and reinstall Vista, but I don’t really want to do that. Would setting a restore point at a known “good” state be enough?

I guess another question would be: could this be symptomatic of some larger problem that might rear its ugly head (some sort of hardware issue?).

Thanks for any insight.

Short of reinstalling Windows, there’s no fix for this if the problem is intermittent and goes away after a reboot or three. If the problem is acute, and it doesn’t go away after any number of reboots, I think there are some fixes for that.

Are you on SP1 or SP2 yet?

I would take it as a sign to perform a clean install of Windows 7.

Running a Vista at all is a sign to perform a clean install of Windows 7.

every now and then Windows seems to think it’s been altered and is no longer a legitimate copy.

You can’t hide forever, taffer. (install Windows 7!)

Time to get a new computer!

Yeah, don’t you know we are in a recession? It’s just Microsoft doing its part to stimulate the economy, so buy a computer already!