GUI Freeze after sleep mode

Hi,

This is my first post because here after searching your and other forums.

I've got 2007 aluminium iMac that freezes up after sleepmode and normal use. The spinning beachball appears and the GUI get's stuck. Only the cursor moves. Only a hard reboot get's the machine online again.

I tried the following:

• fresh system software
• checked all firmware updates
• reinstalled the original ram modules
• installed a other hdd
• ran several tools like TechTool deluxe to pinpoint the problem

None of the above helped. I extracted code the following from the Console App. This code is generated after the system freezes up.

23-09-11 17:44:20 kernel ** Device in slot: SLOT--1 **

23-09-11 17:44:20 kernel ** GPU Debug Info Start **

23-09-11 17:44:20 kernel 0x000094c8

23-09-11 17:44:20 kernel 0x000000d6

23-09-11 17:44:20 kernel 0x00000001

23-09-11 17:44:20 kernel 0x00000018

23-09-11 17:44:20 kernel 0x0000d062

23-09-11 17:44:20 kernel 0x00000001

23-09-11 17:44:20 kernel 0x00000001

23-09-11 17:44:20 kernel 0x000094c8

23-09-11 17:44:20 kernel 0x00000001

23-09-11 17:44:20 kernel 0x00000015

23-09-11 17:44:20 kernel 0x00000000

23-09-11 17:44:20 kernel 0x00000001

23-09-11 17:44:20 kernel 0x00000047

23-09-11 17:44:20 kernel 0x00000000

Could it be my video card is the cause of this?

Regards,

Benjamin