hard disk error??

[jambay19]

MY old hard disk is not working so i decided to check it by changing it with a new funtioning hard disk.Now the hard disk which was okey before is not functioning...after the POST is complete i get the message in a blue coloured screen saying UNMOUNTABLE BOOT DISK...should i reinstall the OS and try or is there way way aorund it??
thanks

[Liggy]

boot to recovery console (you will need XP disk) press R to start the recovery console. select the OS more then likely number 1. at command prompt type fixboot, then fix mbr, then exit and restart the machine