I haven't heard of BIOS getting infected with a Virus however there are Instances where BIOS gets corrupted. BIOS corruption might happen due to incorrect Flashing or Updating with software that mismatches Hardware. (Eg. Incorrect Vendors / Manufacturers).
In your case I would recommend to check with DELL's website to see if the BIOS version installed on your PC is the latest. To be on the Safe Side Boot windows to safe mode and Run a McAfee Full scan to make sure everything's fine.
"Do not tamper with BIOS settings as it might cause your PC Unusable if incorrectly handled"
You might also want to run a scan using Stinger, Malwarebytes Free and RootkitRemover, see the last link in my signature below.