You must have come from the PC world. That Mac does not have a BIOS, flashable or no. The ROM really is a ROM.
The common sources of trouble are bad install, bad HD, and bad RAM. Those are easy to check and fix. Logic board and power supply failures are also possible, of course, but if something changed right after you did an install, then the most logical inference to draw is that the install itself is the problem. If the HD had/has bad sectors, then the new install may have attempted to write to those sectors, making things die.
Boot from a floppy (e.g.) and run a good disk utility. Check the health of the HD, and repair any problems found, prior to attempting a reinstall.
The common sources of trouble are bad install, bad HD, and bad RAM. Those are easy to check and fix. Logic board and power supply failures are also possible, of course, but if something changed right after you did an install, then the most logical inference to draw is that the install itself is the problem. If the HD had/has bad sectors, then the new install may have attempted to write to those sectors, making things die.
Boot from a floppy (e.g.) and run a good disk utility. Check the health of the HD, and repair any problems found, prior to attempting a reinstall.