Apple delivered a refurb MP. And I just hooked it to my 30" ACD. Then suddenly the screen froze with digital artifact lines and squares. Only way to release it was to do a hard shut-down. And restart. Looks like its the stock standard graphics card. Is there any know probs with the ATI 2600 Also under Graphics/Displays. it just says ATI Radeon HD 2600 (rather than 2600 "XT") guess its the same card Should I call Apple and get this exchange?