My computer is less than a year old and all sorts of problems have been occuring...

Recently my computer will start but there is no graphic or display and the computer says once at the beginning "System failed mediator"...which i have no clue what the heck it is talking about. I've also gotten alot of event 51 errors regarding paging errors but due to my computer spec and postings by some people on different forums, it may be due to hardware compatibility - and some people say it could be a problem between SATA and mobo (which basically means I'm hopeless) I use my computer mainly for graphics stuff and just simple music/video and work. and everything is up to date.

here are the specs

windows xp pofessional sp2
2 gig ocz gold ram
a8n-sli premium mobo
7800gtx 256mb gpu
amd athlon x2 4800+
two 250 gig seagate sata barracuda hdd
antec true power 2.0 550w psu

I really can't figure out how my computer is always having problems. I've brought it back to the store nearly over 15 times already...and it's been less than a year.

right now i just wish i can see display while my computer is on. I've switched monitors and still no display so i know it ain't the monitors fault. please would somebody kindly give me a direction?