I have been on 9.10 for over a year on the grounds that if it ain't broke, don't fix it. However, I had a spare weekend and figured it was probably about time...

I performed an upgrade to 10.4, and everything seemed to proceed smoothly, so I took the plunge and went for 10.10.

Disaster.

My twinview Nvidia display which had been working perfectly is now broken. On boot everything seems fine, but when X starts and the second monitor springs into life the primary winks out and switches off - almost as if its been put into an unsupported display mode.

The system seems to think there's a second monitor - the nvidia logo is split across the two screens, but it can't seem to start.

Things I've tried:

• Swapping the monitors (one is older than the other, and its definitely the port not the actual monitor)
• Rolling back to an old Xorg conf from prior to the upgrade
• Installing a non-beta driver direct from Nvidia (this seems to start both monitors but then apparently stops boot and causes the second display to 'wink'. Twinview seems non-functional, both displays are mirrors)
• Disabling EDID
• Disabling twinview, logging in and attempting to use the Nvidia config to re-detect the monitors (second monitor is falsely detected and won't go higher than 1024x768. Selecting 'apply' causes one screen to go blank and the other to display garbage)
• googling for about 5 hours looking for similar problems, none of the offered solutions seemed to work

I'm at a loss, and it is looking very much like I'm going to have to go through a time consuming reinstall to downgrade back to the working 10.4.

Any thoughts?