Take the battery out. If it continues to flash with the same pattern, the flash might represent a bios error or diagnostic code.
As most manufacturer's seem to ignore bios altogether in their documentation, you might try a search on the bios version.
Better yet, download
everestfind out what mobo you have , and see if you can find a manual for the mobo. Unfortunately, dell probably altered the bios somewhat but at least it’s a start.
Bill