check to make sure that your LCD ribbon cable is securely plugged in
and also YOU SHOULD NOT HAVE ANY THERMAL PAD LEFT WHATSOEVER ON YOUR CPU OR THE HEATSYNC...

scrape the crap off as your processor is not getting an even contact with the sync...
your fans should automatically turn off after a few seconds after the bios is able to query the processor's thermal probe otherwise you probbably have an overheating problem...
when you put the old chip back in.. did you pull the wire out?