Hey, I got the same problem it's not your dell tower but it's the screen....
cause I took off my cable and connected my Cpu to another screen and it worked, I even tried it on my TV through VGA Cable.... and it works.
The Solution:
Turn on your computer
Turn on the Monitor, if it is white(Blank) then press the power button to turn it off and turn it on instanly.
The Screen will continue to be white, then again turn off the monitor and unplug it.(NOTE: Unplug only the Monitor) Now after one minute plug it and turn it on.
It will work...cause I just did it so that I could google search the problem and I fell on this forum....