Not trying to ramp a company for their computer parts and equipment. And if you check their web site msy.com.au you may also realise they dont even try to ramp their own site. IMO worst looking site for all time!!! But I get all my parts from MSY. In fact recently pointed Buffett to MSY to build his latest business server. Now Buffett recommends it to his mates. Forget to mention that its best to go early in the morning because often there is a queue and you may wait for ages.
Webral if its not memory then thats good.
Next would be your video memory....?
noticed you got two cards.
Could also try the reinstallation of OS? That worked for me but could have been a fluke.