ok getting frequent BSOD is either one of three things. its either a heat problem, a memory problem, or a power problem.
first check the heat. download a program like SpeedFan
and monitor the temps. if there high then buy a new CPU / GPU cooler. for a temporary fix take the side panel off of your comp and put a desktop fan or something pointing in there.
if it is not the heat, next check memory. run a Memtest86
, or switch memory with a friend or swap it with something if you can. if its faulty ram either RMA your current memory or just buy new ones.
if its not the memory or heat, its almost definitely the power. first make sure everything in your computer is properly connected to the power supply. also, if your plugged into a power strip it may not be letting your comp get full power, switch to a direct wall outlet. you can also buy a PSU tester here at newegg or im sure a place like bestbuy would have them also. you plug the connectors from the PSU into it and it reads the voltages . if you can find a friend or somewhere you can get a PSU with higher wattage that would be great so you can swap and see if its fixed. if you find it is power, you will have to buy one with a higher wattage. single rail PSUs are the most efficient and reliable. most truly high end systems would only need a 700W power supply. 700W is more then enough for sli 8800GTs and 4g ram, 3.2ghz CPU, all of it. For an average system 550W is more then enough if its from a decent maker. some good PSU brands include OCZ, Antec and Corsair. if you check and find that the problem is not one of these, your most likely going to need a new MOBO, CPU, or HD. but 99% of the times BSOD/random freezes and shut downs occur its because of power, heat, or memory.
Edit: it can also be caused by bad drivers or an unstable CPU/GPU/RAM overclock. if you check your power, heat, and memory and your still getting problems make sure your video/chipset/audio drivers are up to date and lower your overclocks if you have them pushed to the limit. you can also run a stability test(Ntune has one for instance) and leave it running alone for atleast 30 minutes. if your computer hangs, freezes, restarts or shuts down then it is infact one of you components are either overclocked to an unstabe level or there damaged.