KVM is cantankerous enough via individual PS/2 connections. Individual USB connections I avoid if at all possible. Throwing in wireless over a single connection, well that's just crazy talk...
Try:
- Verify switch is using power adapter.
- Everything is connected with all power off (computers unplugged) and then everything powered up together.
If you're using wireless for the distance, another option would be KVM over CAT5 with standard PS/2 input devices and switch, more $$ though.