I can not turn on or charge my Colby tablet

Firstly make sure the tablets are charging and are charged, if the answer is yes then you can try a soft reset by holding down the on button for 30 seconds to 1 minute. There may even be a tiny hole with reset written by it, push a pin in this hole gently until you hear a click, try starting now...
Without knowing what tablets you have any more advice would be pointless really.....but try these fixes first and see what happens??

Have you tried turning it off and on?

I'm having the same problem with this piece of s**t

If your Azpen A700 tablet won't charge or come on, you got no result trying to reset it, you've got only one option: take it back to the shop where you bought it and ask for authorized repair service, to diagnose cause of failure You even may have still option to warranty service.
Problem is that it's a low cost 35$ tablet so repair service might not be worth to pay, looks rather as a disposable device..

1. Turnn completly off the tablet.
2. With the tablet turned off, holding the return button while turning on the tablet-pressing power button. Keep holding the return button until you see the Hard Factory reset screen.
3. Confirm the hard reset procedure. Once done, simply wait until process has finished-the tablet will restart. This process can take up to 30 minutes, so it's very important that the battery of the tablet is completly charged before attempting the hard reset. If you can connect it to the charger while resetting, even better.

sounds like the hard drive is froze up

my son charged mine with the car charger for higher voltage charge and its working fine now

Try to reset the unit. the battery may be faulty.

RETURN IT.
Touch screens on cheaper tablets are usually less responsive than on more expensive ones, but the tablet shouldn't be doing anything on its own (clicking noise, opening/closing). You have a defective tablet.
While some of the cheaper tabs (Colby, Panasonic, etc.) can be a good starter tablet for kids, they usually have higher defect rates, break down faster, and are are returned more often than better brands such as Samsung, Google, Nook, etc. For $50-$75 more you can get a more reliable and responsive tablet.