Major boot Problems!!!

i have a 2005 G5 2.0 (early i believe) and it is giving me the white screen with the apple. no scrolling circle.. i have also noticed the keyboard and mouse only stays powered for about 15 seconds when i turn it on. also, the apple icon is much larger than usual. i bought a brand new hard drive and formatted it and the same problem occurs with both hard drives. about every 20 boots it will start and work like nothing was wrong but after about 5 mins of use, it freezes and i am forced to reboot it again. the cycle pretty much repeats. i have booted from an install disk and formated and installed the os. every time i do it, it seems to be working fine and then will freeze and not boot again. i havn't ran the hardware test because i dont have an original install disk. is their anyway to download the hardware test?

i have....

-took out and reinserted the ram
-reset the SMC
-reset the PRAM
-tried the safe boot (didnt respond)
-booted from install disk and reformatted disk
-repaired disk

any input will help. thanks!

-phenito

no. its a brand new hard drive.

ok. so i checked the ram and the ram is good. i tried booting it with out the v-card and it still does the same thing. i can tell because the power to the keyboard and mouse cuts out after 20 seconds or so. does anyone know why the power to the keyboard and mouse is cutting out?

just found out its the logic board. anyone got any tips of what this is and how to replace it?

i took it into the apple store and they did some hardware tests on it. yeah im pretty sure i can install it. i just dont know if its even worth spending the time and money to fix it. any one know a site to get a cheap board? ive googled it and the average price is looking around 400.