Inaccessible boot device

Hi,
HELP
I keep having the strangest kind of problem.
I’m installing windows 2000 server on a pent II 266 mhz computer w/256 mg memory w/a new eide hard drive(western digital). After installing all appears to be fine it boots up w/no problems. I could install latest patches and still no problems. When I install service pack 2 or 3 I get a message at the blue screen saying “Inaccessible boot device” . When ever I install any service pak I get this message. Any help would be appreciated.
Any help would be appreciated.