Its definitely your motherboard - take a look at the link below, several people having the same problem as yourself - how old is this motherboard? It could very well be that it is just not compatible with Windows 8.
Go to the link, there are some potential solutions in the comment section. If those don't work, and given that more than 50% of the people who visited that page voted the motherboard as incompatible with Windows 8, along with the fact that Asus doesn't make a Windows 8 driver for that board, you either have to return to Windows 7, or get a new motherboard.
Windows 8 compatibility for Asus P7H55-M LX Motherboard model
Ya i examine the whole link which u given to me first of all thanks for it.... yes 50% people having the same problem but its also showing that it compatible with windows 8.....nad i also tries the solution but they doesn't work...i m getting hopeless now for this issue..windows 8 is very lovely windows so i want to remain on it but couldn't find any solution of it...plz if u find any solution reply me...i m still finding solution...
Ok, if you are willing to continue and try to troubleshoot this thing, I will certainly do my best to help you out. Our next step will be to download a free, well-known, and trusted system diagnostics software, which is Sisoftware's Sandra (approx. 68mb). After you get it installed, we are going to run a few reports and try to figure out exactly what is going on here.
Before we do that, let's try a couple things :
1. Have you tried plugging the mouse or keyboard into different USB ports? If not, take the mouse out of it's current port, and try plugging it into a different one - do this for every unused port that you have available.
2. You said that you used to have a webcam plugged into the USB, did the webcam ever give you any problems?
2a. If the webcam always worked fine, plug your mouse into the same port the webcam used and test it that way.
2b. Again, if the webcam always worked, now try plugging the webcam into one of the USB ports that was giving your mouse/keyboard problems, and see if the webcam still functions correctly.
3. Do you have an externally powered USB hub? If you do, and it's the type that is self-powered (ie., you have to plug it into the wall), try connecting your mouse/keyboard to that.
4. Try booting your computer with only the keyboard plugged in - see if it works - then when you are at the login screen, plug in your mouse at that time -
After you test each scenario above - let me know what happened on each one.