Serial port drops out

I'm sure this has been brought up, but I can't find an answer that works for me.

My arduino Uno can't communicate from time to time. I'll upload a sketch, and it will work fine for 10-15 minutes, and then I'll be able to upload one or two more sketches, but eventually I'll get a "Serial Port Com7 already in use" error. (the Uno is on com7). it says to close other programs, which I do, but it won't let me talk to it. Then after I wait for a while (how long seems random), it talks to it again.

Oh and one other thing. If I unplug the USB cable, and then plug it back in, sometimes the arduino program software doesn't see it. My "Devices and Printers" page shows it, but the programmer doesn't even have the correct port (com7) listed as an option. Again, sometimes it does, sometimes it doesn't...

What's up with that? Windows 7 32bit.

Thanks!

Use Task Manager to close orphaned instances of avrdude and stop double clicking the upload button.