It's not Ctrl + F11...that's why that don't work. You don't give a lot of the info needed to advise definitively, so a stab at your problem try this:-
Follow this, factory re set procedure, this will not work if you haven’t a pre installed OS held in a secure partition. So, you have nothing to lose give it a go.
Switch off your pc completely and clear the working area.
You’re ready to go: - On switching on, from a completely off situation, “immediately and repeatedly” hit (on its own)F11 (can be manufacture dependant e.g. Sony F10) as it runs up, it’ll in time, show/allow you the option, e.g. “Repair your Computer” select this. Answer a couple other obvious questions but, you’re looking for their top option “Full Destructive Recovery” this is what you’re after. Don’t be shy, it will ask many more times, “Do you really want to do this” just keep clicking yes please.
1.This course of action will take about ten minutes and if you haven’t saved the files that you might like to have kept its now too late. Remember, this will take it back to the day you purchased. So, you can install any subsequent personal software, printer drivers for example, at a much later date.
Sit back and relax while it does its thing…then Bing its back and talking to you, to help you set up your newly purchased PC.
I suggest you install your (for you I suggest Norton 3 user from Tesco’s £24, that’s 8 quid each, fit and forget.) or some such anti Virus now. You’ll need to update your system; this can be lengthy, boring and defiantly time consuming. Might I suggest you leave it on, connected, to your modem while you’re in bed asleep while these updates arrive?