If you are trying to enter safe mode, you need to press F8. If you are trying to enter the BIOS (not recommended unless you know what you are doing), then F2 or the Delete key will typically get you there. F11 doesn't do anything that I know of for the boot process.
Another thing to try is to press and hold the power button until it shuts down and wait a minute or so. It should boot back up when you press the button again. It may ask you if you wish to boot normally or go into safe mode. Try booting normally.
If none of these things work, then your best option is to go to a computer repair shop. Depending upon how old the machine is, it may not be worth saving. However, the shops can usually (not always) save the data from your hard drive.
Good luck.