I go through something like this about once every few months. My A4000 will run without any trouble for months, and then at some point will just lock up. It'll reboot, but a few minutes later it's frozen again. The freezing cycle increases until it freezes in mid-boot.
After a mild panic each time, I realize that I might have to push the accelerator down more firmly on the expansion slot, and that usually solves the lockups. I probably should go find myself some better standoffs. Mine are starting to show some wear and tear.
