Java is probably installed but windows can't find the path.
So what you can try is Computer-> right click->properties_>advanced system parameter
In the advanced system parameter tab click environment variable.
In the list below left click on path-> modify and add at the end ";C:\Program Files (x86)\Java\jre7\bin\", of course you change the path if yours is not the same, don't forget the semicolon.
press ok ok ok.
This is for windows 7 so it may vary and the name may not be exactly the same since I'm not using an english windows.
Hope it help