nt boots to blank screen with mylex raid

i am having a problem with acer altos 1100e server.we are using mylex dac960 raid card with ibm ddrs 9.1gb hotpluggable ultra2 wide scsi hard disks.using raid5 with three hard disks.NT4 with SP4 and SQL7.some times when i restsrt the server the server boots to a blank screen after the configuration screen (PIII450,ram,serial,parallel ..etc box). i am not even getting the NT menu screen.we changed the raid card with mylex 1100 raid card but the same problem is coming.we checked up for boot sector virus.no virus found.

we are unable to find the problem.is there anything wrong with the hard disks.raid never broken.pl.help.server is critical. thanks in advance.