If your computer keeps crashing when you play games or when you are viewing/amending your digital pictures the cause of the crashes is likely to be a problem with your graphics card or its software device driver or even the DirectX version running on your PC.
Downloading and installing the latest graphic driver file for Windows XP or Vista might be all that's required to solve your pesky problem. The best place to get a compatible download is from the graphic cards manufacturer's web site.
If downloading and installing the updated drivers does not solve the repeated crashes the processor on your graphics card might be overheating.
Your graphic card should have a large cooling unit which keeps the card at the correct temperature (most current high-end graphic cards are equipped with a large, cooling unit). Sometimes this cooling unit can come loose from the graphics processing unit (GPU), or its fan can seize up. This 
can even happen if a new graphics card is being installed.
If the cooling unit on the graphic card is properly installed, apart from taking the computer's base unit into a repair shop, you'll have to try swapping the components one by one with ones known to work.
To eliminate the graphic card as the cause of the problem, start by replacing it with one of a different make and model. When the graphic card is eliminated as the cause, try a different power supply unit, followed by different RAM modules. If there is more than one RAM module installed, you could try using only one, because a PC can operate with only one DDR RAM module. Try using each module on its own.
If the PSU and the RAM aren't faulty, that leaves only the motherboard to replace.
But before you try using another motherboard, try re-flashing the BIOS on the existing one with the latest file from it's manufacturer's site. You can also try experimenting with different BIOS settings. It could be that your graphic card doesn't agree with one or more BIOS settings. The Definitive BIOS Guide is a recommended site for information on optimal BIOS settings.
If you want to swap components yourself one way of doing this is to use ebay to buy the components you need (e.g. motherboard, processor, RAM, Power Unit) and when your tests are complete resell them. You might even make a profit!
Downloading a DirectX version that is not compatible with your graphics card can make your PC keep booting into Safe mode. For example, if after having installed some gaming software your system starts crashing, and then will only boot into Safe mode, the chances are that you installed the latest version of the gaming software driver DirectX 9.x, and it's incompatible with your graphic card's drivers. For this latest game installing DirectX 9.x will probably have been required, and as such will have been provided along with the game and installed along with the game software.
To rectify the situation, you will have to find out the make and model of graphic card that is installed in order to download the latest drivers for it from its manufacturer's web site - or from the chipset manufacturer's web site.
If you can boot into Windows you can find out the make/model of the graphic card installed in your PC by using the DirectX Diagnostic Tool. Enter dxdiag in the Start => Run box in Windows XP, and look under the Display tab. In Windows Vista, click on the Start button and enter dxdiag in the Search box.
However, the problem will probably have been compounded, because Windows will install its standard VGA driver in order to boot into Safe mode, so you will not be able to identify the graphic card using the DirectX Diagnostic Tool.
If the graphic chipset is built into the motherboard, you will be able to identify it in the motherboard's manual. If you don't have a manual, you should be able to download a manual from its manufacturer's web site - using another computer connected to the Internet, since the problematic one is out of action.
To identify a graphic card for which you have no documentation, and which is installed in either a PCI or AGP slot on the motherboard, sometimes you can find out its make and model from a printed label on the card itself, or you might be able to read that information from the Start-up boot message that usually flashes by too quickly to read.