In some Dell models there is also the "F10" (If I'm not mistaken) key to access the recovery partition.
But most times this is a question of timming with the Crt+F11 shortcut.
here is a good guide for the multiple options of recover you might won't to try, and also pros and cons of each :
Turn on the computer, at the "Dell" splash screen hold down CTRL and press F11. Let go of both keys.
I think the trick is to hold CTRL just after you turn it on and then press F11 a few times... eventually you'll get it