Got in and switched my main computer on and all it says is please put in a boot device

Put a win XP pro disc in and it loads files but then it tries to start but i get this:-

Blue screen writing with this

*** STOP : 0X0000007E (0xc0000005,0xF853D0BF,0xF8989208,0xF8988F08)

*** pci.sys - Address F853D0BF base at F8536000, Datestamp 3b7d855c



HELP???