Servers will not restart

Abouth a month ago I applied Windows 2000 sp3 to all our servers. Three servers have identical problem after the service pack was applied with Windows update from the web:

Three servers will not restart.
Every time you choose: shutdown and restart option, the servers save all settings and a blank screen appears with a single dash blinking in a top left corner of the screen. It stay like that, we must power it off and on in order to have them restart. I down loaded the latest bios.
That didnot help. All of our server are HP Netservers LH4 with dual power supplies.
Do you have any ideas what could be causing this and how to fix this.