I've started having occasional trouble with my mouse. It's an A4Tech Run On Shine optical mouse. What happens is that the mouse lights up during POST and stays lit when I'm presented with the boot menu (Grub or whatever it is) but when Linux starts to boot the mouse goes dark and won't work from that point onward.
It happened a couple-three weeks ago, so (using the Synaptics touchpad - yech!) I did some research and ended up running the upgrade from Synaptic package manager. As soon as I launched Synaptic the mouse started working again. I figured maybe for some reason entering the root password fixed it? I went ahead and installed my updates and all was joy.
This morning it happened again- powered on the laptop, let it auto-boot into Linux, went to select my user name from the login menu, and no mouse (the cursor didn't move and the mouse wasn't lit.) I hadn't changed or done anything since shutting down the computer yesterday evening, when the mouse was working. Today, unlike last time it happened, I had some extra troubleshooting tools at hand: I'd reinstalled PCLOS as well as Vista in a dual-boot configuration, and I had an extra USB mouse at hand.
I powered off then removed every other USB-connected device (external HD, USB-powered speakers) and tried again: no joy. I booted with even the mouse unplugged then plugged it in after PCLOS was running and I was logged in: nope. I booted into Vista and the mouse worked, so I knew it wasn't a hardware issue. Booted back into PCLOS and swapped mice- it worked! (so I knew my X11 config files were probably OK.) Plugged the A4Tech back in: failure.
I did some more research and read that A4Tech mouse drivers are part of the newer Linux kernels, so I installed the next-older kernel to try (I have 126.96.36.199 and I installed 188.8.131.52). Booted into that older kernel and noticed that the boot process took a lot longer than usual, and also noticed that my mouse's lights flashed a few times during boot as though it was being detected. The mouse worked when booted into the older kernel!
I booted back into the newest kernel I had and the mouse still worked. I did a complete removal of the older kernel, rebooted, and lo! The mouse still worked, and continues to do so. So it seems there's an intermittent bug in the 184.108.40.206 kernel that occasionally causes A4Tech mouse detection and/or its drivers to fail.
(By the way, all boots/reboots were actually shutdowns and cold boots, just FYI.)