Would need to look at the machine to troubleshoot.
So happy reading and good luck with it.  Expensive mistake unless you can do the repair yourself. 
http://www.pinrepair.com/sys1/index.htm

Get your parts from here.
http://www.greatplainselectronics.com/
http://bigdaddy-enterprises.com/index.htm

Makes sure that whilst you are at it, to do all the mods if they haven't already been done.

If your cpu board is original you might need one of these.
http://www.ni-wumpf.com/System1CPU.html