Hello Jolanda and welcome to the forum.
Some additional information, specific to your particular computer might be helpful.
Manufacturer's Name, Model Name, Model Number (complete model number)
What keyboard you are using? How is it attached (wireless, USB, integrated as in laptop)?
Do you have any associated drivers / software packages installed to support the keyboard?
There are a number of third party software programs that facilitate the assignment of keyboard shortcuts (home key opens browser, assigning "favorites" to hotkeys, etc.)
You may want to try clean booting your computer to see if the problem persists in a clean boot state......
https://support.microsoft.com/en-us/kb/929135