Slow Reboot

We have an IBM Netfinity 6000 with 4x Xeon 700 CPU’s, 2gb RAM, 144gb RAID, running w2k Advanced Server, MSSQL2k, with all latest service packs for all that is set to reboot nightly at 0400. The problem is it is taking till 0530 for the system to come back up. Any ideas on what could be causing this?