I've had a wired Dell mouse that has worked fine for years. I decided I wanted to use a wireless mouse. When I put the wireless receiver on my desktop and use the mouse on the desktop it works fine (with the wired mouse still plugged in). When I put the wireless mouse on the mouse tray next to my keyboard and slighly below my desk, it work erracticly UNLESS I keep my wired mouse next to it (and plugged in) If I remove the wired mouse, the wireless mouse will not work when the receiveer is on top of my computer, which is underneath my desk, and my mouse is on the mouse tray (also under the desktop), which is my preferred position for the mouse. I don't want to use it on my desktop as it's uncomfoprtable there. Any suggestions?