Re: ibm thinkcentre restore
You may not be pressing F11 at the correct time. There is only a short period during which F11 will respond as expected, and that's usually at the manufacturer's splash-screen just after switching on.
Remember also to "press and hold" F11. A single jab or repeated jabs may not be sufficient. I have to press & hold the appropriate key on my PC as soon as the splash-screen appears.