Win98 no boot excpt cmd prompt only mode

Celeron 533 PC with win98.

When system boots it gets the Win98 startup bmp then powers off after about 1 sec.

Does the same in “safe mode”

Only way to boot is in “Command Prompt Only Mode”

When I tried a logged boot (bootlog.txt) no bootlog.txt is generated and it powers down.

Am running a virus check – what else should I check?