Some years back I had a case where a co-worker complained his mouse didn't work in the afternoon. Eventually I went to have a look, and he demo'ed the issue; sure enough the mouse was completely unresponsive. Luckily I guessed the issue immediately and quicky demonstrated - with a shrug - that the mouse "works fine for me".
Thing was I'd spotted there was strong sunlight through the window hitting the mouse; guessing it was probably swamping the optosensors I made sure I covered the side of the mouse with my hand when using it. His puzzled looks as the mouse worked for me but not for him were priceless (I did let him in on the secret after a few minutes).
Thing was I'd spotted there was strong sunlight through the window hitting the mouse; guessing it was probably swamping the optosensors I made sure I covered the side of the mouse with my hand when using it. His puzzled looks as the mouse worked for me but not for him were priceless (I did let him in on the secret after a few minutes).