Hello hopefully I can help you in getting this problem solved.
Your computer may have been damaged by a possible power surge, true you had a protector in line, but that does not always protect you from a component failing that was possibly on the verge of going eventually.
Here is some support options I have found from Dell that you can try, start with the first link then the second one if first suggestion fails.
This page below was designed for both laptop and desktop computers, if you pay close attention, you will notice some information is for laptops and some for desktop computers, please stick with laptop information only.
If nothing at this site solves the problem, your laptop will need to be serviced for internal component damage, most likely diode or capacitor related.
Its either that or your power supply has an internal fuse and the surge blew that fuse out, but in a case like this, the laptop should still start off of the battery.