Erratic Wii Remotes
You may find that when you point your Wii remote at the screen the hand that acts as a cursor behaves erratically, such as appearing somewhere you are not pointing, shaking when you are holding the remote still or even disappearing completely from the screen. This could mean the batteries need changing or there could be a smudge on your the front of the remote. If these are not the cause, then re-sync your controller and adjust the sensor bar sensitivity from the Wii Settings menu.
Overheating
If your Wii is turning of unexpectedly after running fine for a while it is likely that your console is overheating. This can happen if you use your Wii in a closed space; or, if it is stood up vertically in its stand, the vents may be wrongly aligned with the hole in the stand. Correcting this should help the issue. Built-up dust could also cause this problem, study the vents on your Wii for signs of this. A vacuum cleaner with a soft brush attachment should be able to remove the dust.
Not Playing Discs
If the Wii is not reading the games that you put in and you receive an error message like "Unable to Read the Disc," your system could need a repair as the optical lens that reads the disc may be contaminated or broken. However, there are much less serious causes for this issue, one being that your Wii console is upside down, as this is in an easy mistake to make. Inserting the disc the wrong way would also cause the same problem. Furthermore, there could be a problem with the particular game you are using, in which case you should test out another.
Won't Turn On
If the Wii will not turn on and there is no light on the console, there is a problem with the power connection. The AC adapter -- the Wii's plug -- may not be inserted far enough into both the plug socket and the back of your Wii, or the wall outlet you are using could be faulty. However, if the AC adapter has been attached firmly and the outlet has been tested with another electronic device, there is one more fix you can try before you purchase a new plug. Remove the AC adapter from the wall and Wii and repeat this action with any other cable or device attached to the console. Plug the power cable back in after waiting two minutes and check to see whether there is a power-supply light on the Wii.