If you made it this far and your computer is not brand new:
Its a good idea to do some spring cleaning before you point fingers. Download CCleaner and Spybot.
In CC cleaner, select all of the options except "wipe free space" and Analyze/Run multiple times. Then flip to the registry tab and Scan/Fix multiple times. (You can save a backup if you want to. I never have felt the need to do this.)
Both of these will find different things if you run them multiple times. I usually do each repeatedly until I get no results, then restart and keep repeating the cleaner and registry parts until I get no results again.
Then have spybot do a full system scan and select the option that allows it to scan before you log in to windows, remove anything you do not recognize. If you are more familiar with a different antivirus, feel free to use that.
New or not, time to test the hardware:
If you are still having problems at this point it is likely the overclock or the hardware itself is failing. To find out which it is we will need to troubleshoot.
*If you can pass Prime95, its likely related to software. Skip the rest of this paragraph.
*If you had to reset the BIOS to pass Prime95, the overclock was unstable. Post in the Performance / Overclocking section or contact DSO directly for help tuning it up.
*If you do not pass Prime95 even with the BIOS reset, it is probably hardware, so we need to test it individually.
*If you fail this test or have errors with your BIOS reset, the RAM could be faulty. Contact DSO directly for further instructions
*If you pass this test with your BIOS reset, it could be the processor.
*If you fail this test or have errors with your BIOS reset, the CPU could be faulty. Contact DSO directly for further instructions
*If you pass this test with your BIOS reset, it could be the power supply, motherboard, or software related, post in the Technical Assistance section with everything that has happened and everything you have done so far for further assistance.
If all of this passed, your problem could be your video card.
If you pass the video tests, move to the next section.
Stability problems when using the computer (not gaming)
If your system is overclocked, you have to rule that out first, so as discussed, see the bios reset section first. When you complete that part, if you are still having problems, then come back here. its time to start shooting from the hip, troubleshooting software can take some work: first step is to roll windows back to an earlier date, probably about 1 week or more, avoid installing windows updates unless you find out that something else caused the problem.
Lots of people have drivers install automatically(maybe even without knowing it), check your drivers to see what has updated recently. If you find anything has updated pretty close to the start of your problem, look online for an older version of that driver, then see if you still have problems. If you dont know what has updated recently, check through your Device Manager(hit start and type Device Manager) on the driver tabs and see what may have had recent update dates.
If you dont make any progress, post on the forums with everything that has happened and everything you have tried, software can be very tricky. Be sure to include as much information as possible.
Stability problems when using the computer (gaming)
*You must remove any overclock on your video card if this is one of your problems. Not only do you need to rule it out as the cause, but the excess heat could cause damage to the card.
**Also, if you are using SLI / Crossfire, remove all but the highest up video card. Best to just rule out this causing your problems from the start.
This section will assume you are having problems with more than one game. If everything but one game works, focus on that game first, I would suggest looking for problems in at least 2 different games before changing anything below, some games just have bugs and glitches that cause you to crash or freeze. Recreating the issue in a different game ensures that the problem is more than just that specific game. The best tool for this is Google, if its game specific, its likely not going to be just you having the problem. You can also contact the game creator to see if they are any help.
Most problems with games only lie in unstable overclocks and video drivers. The easiest thing to check for is a software conflict or driver issue, so first go to nvidia or catalyst website, check to see if your video driver is up to date. If the last release is the driver you are still using, go back about 2-3 releases and install an older version. Try your game again and see if you have any problems.
Heat Issues:
If your screen is artifacting, or your computer is just shutting down (without a blue screen or an error) its possible that heat is causing your problem, its a good excuse to clean out your case(if it is not new), dust can cause serious heat problems that get far worse and harder to clean as time goes by. Take your case outside, preferably when it is a little windy. Remove both side panels using the thumbscrews on the back, use a can of air duster, found in the electronic section of most stores, to blow everything out. The more thorough the better AND the longer until your case will need it again, focus mainly on your video card fan/exhaust and your cpu heatsink and fan.
If your computer is new and your temps concern you, pick up RealTemps and have a look, if you are getting over 85c at any point, use a flashlight to check each fan while the computer is on to make sure the fans are spinning. You can also hold your had out infront of the fans to see which way the air is going. If you have a liquid cooled system then look at the tubing to make sure the liquid is moving, and make sure your reservoir is close to 3/4 full.
Again have to rule out overclocking causing the issue, see bios reset section to return your settings to default. If you can play games without problems when the bios options are reset, your overclock was either unstable or it could have been causing too much heat.