I can install my labtec media wireless desktop 800 on my pc.

That unit is old just buy a new one

Most of these are brand specific. If the unit is bluetooth (I don't think this is the case) , you can buy a dongle, no problem. If not, you can try to find a used on for sale. You can buy a basic wireless keyboard and mouse new for under $30.

you have to disconect the conection and conect it agian and if it fells to conect you can go for another label media 800

google it download the drivers , alldone

you can check your usb driver 

it's work or not 

you can go to control panel after that system device and hardware 
and check proper install or not 

There are drivers available here

http://www.opendrivers.com/freedownload/248954/labtec-media-wireless-desktop-800-v6.0-windows-vista-xp-2000-download.html

you have to install the driver for the keyboard in order for multimedia keys to work

Check the batteries in the keyboard and in the usb hub. If they are dead, the keyboard will not be recognized by the computer. Replace the batteries and stat the machine. Battery replacement should be done w/the computer off.

Did you receive a install disk for the keyboard and mouse. typically you need to run the install disk and then plug in the usb hub for the keyboard and mouse to be recognized by the computer. If tha does not work, restart the machinew/the usb hub and keyboard and mouse ready. Are there good batteriesin the keyboard, mouse and usb hub?

Go to:
http://www.labtec.com/index.cfm/service/listing/EUR/EN,crid=68,crid2=1762
to update your driver software.