You must always follow the BIOS instructions exactly... and what you described is posted for the E510. The safe way is to flash the BIOS from a floppy DOS disk, as that prevents this problem usually... but many E510 machines do not have a floppy drive.
Here is what the Dell site says for the E510:
"NOTE: Shut down all other applications prior to running the BIOS update utility. The update utility reboots your system in order to get the new BIOS loaded.
Run the BIOS update utility from Windows environment
1. Double click the Icon on your desktop labeled D5150A07.EXE.
The Dell BIOS Flash window appears
2. Click the Continue button.
The message Pressing OK will close all applications, shut down Windows,
Flash the BIOS, then reboot. appears.
3. Click the OK button.
The system will restart and the BIOS Flash will be completed.
Run the BIOS update utility from DOS environment (Non-Windows users)"
If you are under warranty, or if you followed the above instructions, they should not charge you the $150 for the new motherboard.