Clear nvram through advanced mode of SCU, and reconfigure properly. You should follow the directions closely as there is a specific way to "properly" clear out nvram and reconfigure cleanly. nvram.html
Pull out all non-essential expansion cards (PCI/ISA/EISA/...). Run for a while and see if the problem still exists. Remember to run SCU (F10 utility) after making hardware changes.
If the problem still exists, try pulling out ALL expansion cards (PCI/ISA/EISA). Run for a while and see if the problem still exists. Remember to run SCU (F10 utility) after making hardware changes.
If the problem still exists, reduce the CPU count to 1, and run on the minimum amount of memory the server will support. Remember to run SCU (F10 utility) after making hardware changes.
If you still have problems then run server diagnostics (accessible through F10 prompt, or you can boot to them).