Hi raymansz
You get that error when the hard drive access mode changes, this can happen if the cmos battery is flat and you let the main battery go completely flat.
By default most Dells set the hard drive access mode to Raid, why i don't know. Anyway try setting to achi or ide and check the date and time are set correctly in the Bios.
If it still doesn't boot then there is Patio's Suggestion of a repair install.