Check also that it isn't an over heating problem
I'll second that. If you're using a CyberstormPPC, check that the fan still works.
Antec (and a few others, probably) sell these great little cooler units that use a free backplate card slot. They're great for Amigas since standard coolers won't fit without some casework. If you have a free and/or extra slot available, I would recommend one. My 1200T has been about 10x as stable since installing one.