So as I was playing Minecraft tonight, my computer screen started getting really glitchy, and forced my computer to restart. My computer then kept turning off and restarting, but could never get past the loading screens (All of which had blue lines running / glitching about them). Eventually it moves onto a black screen for a bit, rinse, repeat.

Anyone have some advice?
I may try using a different computer screen, to see if it's just a problem with the monitor. I doubt it's going to be that easy though.

I havent had that happen to mine so it may just be the monitor

my old computer used to restart every 2 hours or so but no blue lines or anything like that.

Hmm check your vid card make sure it anit fried it self up and if thats ok have a root round your motherboard a chip might have blown or something like that.

I would say it would be a video card, there is a way to find out if there was a blue screen though:
Start > Control Panel > Administration Tools -> Event Log.

Go onto the 'System' log and scroll down to about the time the restart happened and look for an error. Double click on that error and look at the description, it should tell you what process/hardware crashed.

A similar thing happened to my old computer, and unfortuanately it looks like it could be the graphics card is on its way out.

Cheap graphics card on ebay me thinks!

I'll concur with the vote of the graphics card. Failing that, check your power supply and make sure your computer's on a surge protector.

I've done tech support for years, primarily with monitors... so I can say it is definitely NOT the monitor, they are dumb devices that have no impact on the operation of the PC (cannot cause a restart at all).

Its probably your video card. Full screen apps like Minecraft tend to use a lot of GPU cycles and heat up video cards. This can cause fans to fail or chips to burn up. Also, just random defects in video ram can cause the problem you are describing. Also, sometimes the electrical connections between video cards and the PCI slot can suddenly become degraded. If you have a video card and not a built-in video chipset, try pulling the video card out of the motherboard and re-installing it. Also, some video cards have a separate power tap from the power supply powering the card, pull that off and re-seat it as well.

If you leave the computer off for around 10 to 20 minutes, does it boot up ok? If so, it could be a heat related issue. Check that the video card fan is still functional. If it is, check that there is proper airflow around the fan (blast the dust out of the heat sink). Note that not all video cards/chipsets have fans.

If there are still problems even when cold-booting, then the video subsystem is probably fried.

Its fixable, though. You can disable on-board video systems on 99.99% of most computers (if your video is on-board), and install a new video card in one of the expansion slots. If you don't have on-board video, then the video will already be on an expansion card (referred to simply as a "video card"). Just swap the video card with a new one and re-install drivers for the new card.

The computer doesn't boot up completely, just stays at the loadings screens and continues to restart. I did leave it turned off all last night, and tried again this morning, with no luck. (I'm using my laptop right now in case you were wondering.) So I don't think this is a heat problem, and it hasn't overheated in the past either.

Can you boot into safe mode at all?

http://www.flickr.com/photos/55910355@N03/5582629414/

*Black screen*

http://www.flickr.com/photos/55910355@N03/5582044749/

Apologies for the quality, but you can't expect much from a 2.0 mega pixel phone camera!
Hopefully this'll give you and idea of what's going on.
It's just this cycle over and over.

It's possible that the overheating may have fried some components irreparably.

I just took of the side panel and had a look at the video card and power supply. Everything was plugged in, and I made sure the card was pushed in all the way. Since the video card is a bit too large for the computer, it occasionally gets loose.
So I put back the panel and tried to boot up again, but was still yielding the same results.
(By the way, it does have its own fan.)

Its as blaack as a black mans cape.

I would say video card. You should in theory be able to run it with out the graphics card. Ie remove the card and see if it has an effect.

It looks like a graphical error of some sort.

Not the screen, screens just go.

So, remove additional graphics card. Let it run on the integrated graphics. If it works, then you need a new graphics card. If it doesn't. Probably a motherboard issue.

Well I wasn't able to test the integrated graphics (Best Buy sold me the wrong type of VGA cord) but I should be getting my hands on a decent video card fairly soon! (Someone I knew had an unused one, just wasn't brand new.)

Thanks for all your help guys!

Nice one, see you back on the server soon!

In the event that replacing the graphics card doesn't work, I highly recommend you try switching out the hard drive. Not long ago I had the -exact- same problem, where my computer would continually reboot itself, only going as far as the Windows XP splash screen, pictured here. I sent my desktop to a friend who usually does all my hardware repairs since I've not the courage to touch the tower with a screwdriver and what he found was that all the parts were fine, but when he switched out the HDD it would run as normal without rebooting. The culprit we later found out was a virus, a Trojan in fact that had been hiding away in the Windows System files. Had to completely format the drive to save it. Hope that helps if it turns out you've got the same problem as I did.