The socket type of both processors is the same PGA478; they fit the motherboard socket; however, it is necessary to check with your laptop manufacturer if the BIOS of the board contains the microcode of the new Intel® Pentium™ P8800.
It seems the processor is not recognized properly and BIOS sends the alert to shutdown the system.
@mikec_intel thanks for the answer.
My laptop is Toshiba A300-276 PSAGCE and i went to see in the toshiba forums and asked the same thing. I had an answer from one user there saying that toshiba doesn't support cpu upgrades and is for users own risk to change their cpu... Not a single info of "inside H2O 2.20" bios version -.-
I searched also for a place to write to toshiba support but the automatic support sends me to forums...
i'll try to search for it again.
One more thing, i found in several places that computer going down either at the beginning or at windows login screen is many times related to a capacitor "Nec Tokin OE907". Don't know if this is the problem.
After i reset the bios to try another solution, p8800 still wouldn't work but when i switched to t4200, it had the same problem as p8800 and went down, next i entered in security mode and rebooted, after that the old t4200 worked again...
I really think this could be a nec tokin capacitor issue, it happens a lot in toshiba laptops from several models that have this capacitor.
Well' thanks again for the answer mikec