...yet more problems

okay, i built my computer around this time last year and last october a problem occured with my cheap PSU (which came with the case) and it took out my graphics card, motherboard, and memory. I just recieved my new memory today and installed it. at first, the computer booted up but froze when it reached the "loading Windows" screen. so i resetted the CMOS and that only made things worst, now when i turn my computer on, a few secs later it shuts itself off. so i made another attempt to get it to work and took everything out, then rebuilt my computer but i still encounter the same problem. Im hoping some1 could shed some light on this subject, since i have tried all that i could think of. any help is apreciated, thanks in advance.


------------update--------------
well, ive been working on the computer since i posted this and i got it to stop turning itself off, but now even though it runs i get no video and i get the beeps from the motherboard saying that there is a parity circuit faliure.....how do i solve this?