Wumply....try this as well...

DONT try pressing the keys all at the same time.

INSTEAD...press and hold the CTRL key, then press and hold the ALT key...

once that's done, press and release just the DEL key (while still holding down the CTRL+ALT keys)...if it still does not work...use the other CTRL, ALT, and DEL keys. The other DEL is above the arrow keys or on the numeric pad on the right side of the keyboard and the CTRL and ALT keys are in the left and right corners of the keyboard.