I have a 486Dx33 with VESA local bus and AMI-bios and it just won't boot. The screen stays black and i don't even get a "beep error code". I have tried to discharge the CMOS, turned off the machine and press the ins key and all ohter well known tricks. Nothing happens. Once the setup menu came up and then the machine locked up. What to do (I don't have access to a POST-code card).