1. Boot server in safe mode to see if it is a network/iSCSI/3rd party service or driver issue.
2. Disable the iSCSI NICs from within safe mode and see if the server will boot into normal mode.
3. Enable one iSCSI NIC at a time to see if there is a possible hardware issue.
4. Remove MPIO and Present iSCSI disks down one path.
5. Remove any newly presented iSCSI disks to see if it is an issue with new storage.
6. Configure machine to manually generate a system crash and collect a complete memory dump using CTRL+Scroll+Scroll durring the slow boot period.
972110 How to generate a kernel dump file or a complete memory dump file in Windows Server 2003
If the issue happens even though the iSCSI NIC’s are disabled, you can use MSConfig to disable 3rd party services and startup applications to isolate the service causing the issue