I had problems getting it to work reliabily between two open-plan rooms - a distance of 40'. I found moving the transmitter that is connected to the PC higher helped. I used velcro to mount it as high as the cable would allow (you could use a USB extender cable if necessary).
Bear in mind it could also be other 2.4Ghz equipment interfering - e.g. WiFi, wireless phone or video sender. Moving this type of equipment may help.