Chosen Solution
Hi. Video card is GeForce GTX 660M (if needed). Upgraded HD to SSD and decided to refresh Thermal Paste as computer is 8 years old and hasn’t been open (screen adhesive seems to be original). Now screen resolution is at 1280x720, everything is pixelate. Even Apple logo on startup. Going to System Preferences - Display shows Only resolution mentioned above. No Other Resolutions are listed. Did I somehow damage Video card by reapplying Thermal Paste? I work in computer repair shop so have done it zillion times. Thank you for taking a look.
Did you try running diagnostics? Restart your system and press the D key to enter Reference: Mac startup key combinations
Had the same problem. Tried everything from reinstallation, resetting PRAM, SMC, etc. Been on call with Apple support for a half an hour. Unable to run diagnostic, not even remotely or from a flash disk. Nothing helped. Brought the iMac to an authorised service centre here in Brno, CZ and they quoted me €700 for a new LCD. Which is a basically price of the whole iMac…
