Hello and welcome to Bleepingcomputer.
First a link to your owners manual in pdf format. http://www.csd.toshiba.com/cgi-bin/tais/su...mily=1073768663
That link also has other support information that you could use.
It is to my understanding, you dismantled this laptop to replace the main-board.
In rebuilding the system, did you take extra care to recheck those ribbon wires with the ZIF connectors to be sure everything is snug and making a full connection?
Laptops are one tedious device to assemble and it doesn't take much for one of those ZIF connectors to pop open breaking the connection.
I don't really think the problem you had with the other board may have caused the CPU to be fried. Or if it did, there had to be a serious short circuit somewhere.
Hope this helps.