I get the grey screen after startup on 2006 macbook pro. no keys work.
Sounds very much like the graphics chip is on the blink again, it's pretty common to see these units fail again and again...

Unfortunately you won't be able to get it serviced any more as it's classified as obsolete by Apple now so no parts are available, although maybe eBay etc...

There is a chance you could do an OS reinstall to verify it's a hardware fault and not software, but the diagonal lines is symptomatic of a hardware graphics chip issue like you would see on this range of machine.

I would be looking to replace the machine at this point sadly. It might be worth going to the manager in an Apple Store and indicating that it's failed for a known fault again and asking if they would give a discount on a new machine as they may well do this as a gesture of good will.