my laptop was automatically reboot while while my usb drive inserted, i removed it and press enter, then the error operating system not found appeared, I'll switch it off and on again but the same error was displayed, "operating system not found"
Sounds like in your case press F2 and see the "setup". See if the hard drive is even there. The setup should be the boot order. That will tell you if the hard drive is detected and that will be a good place to start. Then you can go with those instructions. They are for an HP desktop but the idea is the same.
Well, yeah. But the way he described it sounded as if he could not... We need more info from him.wouldn't the easiest thing to do first was to enter multiboot (f12) and see if he could in deed boot from the internal hdd? he could have had his bios set up to boot from something either than the hdd first (cdrom, external)--maybe. that has happened to me before--if i have the bios set up to boot from something other than the primary hdd first, and i accidentally leave an external hdd plugged in, then i will get a "cannot find operating system" message. so i have to reboot into bios, select to boot from primary hdd, remove the external, and all is good. try the easiest route first.