I am trying to start my computer and it is frozen on the Dell start up screen. I have tried F2 and F12 as directed on the screen and nothing is happening. I'm in the library asking this and would like not to have to get a professional out to fix it, costing £60 an hour.
Have you switched it off with the power off/on switch and tried again pressing F12 whilst it's booting up? You must repeatedly press F12 whilst it's booting up otherwise it won't work.
If you can do that, select "start in safe mode" then use System Restore to put your PC back to how it a few days before the problem started.