reboot and select a proper boot device also motherboard changed

HELLO
i recently changey my liptop motherboard due to burning of sone main ac.s ,so called the repair man..i googled many problem but result is nil...i try many techniques and help as follow
i changed the boot pririoty to hdd but no result
i used ms-dos for ueif and legacy mode but no sucess
i used safe mode but no result
when i start pc it popup with a very common message .reboot and select proper boot device or insert boot media in selected boot device and press a key

i also use another liptop and with a another liptop my hdd is working properly but why not on my pc .
if you have a any experience solution then plz share with me or it need a fresh window then told me a method that i dont want to lose my activation.
my liptop detail
toshiba satllite c850 window 8
intel core i3 with 2.20 ghz and 4 gb of ram
toshiba hdd with storage of 320.
i am waiting for your kind reply

It's rare that Win7 will boot with a mobo change because the hardware difference is too great. But you may be able to adjust it using this boot disk to Adjust Win7 to boot on new hardware with Paragon Adaptive Restore CD.

I doubt whether activation will hold though because change of mobo almost always causes deactivation, and once you change mobos the Product Key on COA sticker no longer will work because the hardware change is considered too great - unless you change the mobo to the same model.

It's possible that it may by a fluke hold activation, or that MS may allow it if you use Phone Activation after it deactivates and rejects the key.

thanks for your reponse .
my pc does not go on window and how i apply the paragon adaptive cd tool ..
and i have window 8 install in .

Click the blue link to read how to burn and use PAR.

If this doesn't help then I'd ask over at Windows 8 Forums