I tried upgrading my HP 520 laptop from Celeron M 440 to dual core T2450. The BIOS detects the new CPU but laptop won't boot and there's no display. Place the Celeron back and it boots fine. What's wrong?
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Did you do a BIOS update before you changed CPUs?
And you did check to see that the dual core T2450 CPU was supported by your motherboard?