Try this first
Items in blue which are underlined are clickable to give more information about the process
Start the System Restore Utility at a command prompt
1. Restart your computer, and keep tapping F8 during the initial start-up until you get options, select Safe Mode with a Command Prompt then press enter.
2. Log on to your computer with an administrator account or with an account that has administrator credentials.
3. Type the following command at a command prompt, and then press ENTER:
%systemroot%\system32\restore\rstrui.exe
4. Follow the instructions that appear on the screen to restore your computer to an earlier state.
Look for the most recent system checkpoint created before the errors to restore from
For additional information about the Safe mode with a command prompt, click the following article number to see a description of the Safe Mode Boot Options in Windows XPthe article in the Microsoft Knowledge Base: 315222
Try tapping F8 as you boot to see if you can choose safe mode
Alert! Previous attempts at booting this system have failed at checkpoint [nnnn]. For help in resolving this problem, please note this checkpoint and contact Dell Technical Support.
The system has failed to complete the boot routine three consecutive times for the same error. See "Getting Help" for instructions on obtaining technical assistance, and report the checkpoint code (nnnn) to the support technician.
From their forums
VMGR is the PNP/PCI configuration checkpoint. Try removing the scsi card or any other PCI devices to see if the system will post.
This is for their support wizard
http://support.dell....=dhs&treeid={0}