Hi Marco,
Thank you for contacting Microsoft community. We will be glad to assist you with your concern.
From the description mentioned, you are unable to access some keys and space bar from the
Microsoft Wireless Comfort Keyboard.
I would suggest you to follow the methods to fix the hardware issue.
Method 1: You may try to run the Fixit.
Hardware devices are not working or are not detected in Windows
http://support.microsoft.com/mats/hardware\_device\_problems/
Method 2: Follow the steps in the link to fix driver issues
Tips for fixing common driver problems
http://windows.microsoft.com/en-US/windows7/Tips-for-fixing-common-driver-problems
Method 3: Try to connect in clean boot mode:
Clean boot: To help troubleshoot error messages and other issues, you can start Windows by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate
software conflicts.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135
Note: When the troubleshooting is over do not forget to reset the computer to normal startup. Follow the step 3 in the above article.
Post back with the result. If the issue is still not resolved, I’ll be glad to provide additional options.