ok to boot from the disk you should enter your bios by pressing F2 setup(button may vary you should find it in the top right of your boot screen) then scroll to boot configuration open that up and...

run system cd and it will repair all of that

do a system restore to a point before this problem occured (if possible at least 48 hours before) goto start<all programs<accesories<system tools<system restore then pick the date. now after your...