Why does my tablet just show a red battery when I turn it on?

It is possibly that the cord may be broken. You can bring it and your tablet into most electronic stores (even Best Buy) and they can determine whether it is the cord or your device that is the problem

It comes on but all it shows is tablet pc, it will not show any of the apps.at all. I want to know is what is wrong with it? The battery is charged.

The charging light may come on but that does not mean the battery holds a charge....have the battery checked

The tablet was either accidentally turned on and didn't shut off automatically as it should have or it has sat in a warehouse somewhere for 2 or three years. Contact the retailer and get a replacement.

This is most likely your battery that needs to be replaced. A bad battery will show fully charged and not have enough juice to start the device up.

Check its charger. If the charger is faulty, it won't charge the battery. If it is found OK, replace the battery. It is bad.
If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/

Most likely the battery is shot. If you could, try to power it up with the adapter supplying power. If this is successful it indicates that the battery is done for and no longer holds a charge. Most of the batteries on small, inexpensive tables only last for a couple of years. Yours may have used up it's life waiting in a warehouse. I have generally been unable to find replacement batteries for these tablets. There is a company in China that makes most of them as custom runs for small companies and does not stock replacements. You may also try to do a "factory reset" while the "powering up" logo is showing, find and press the reset button while using the power adapter for juice. If you manage to get it to run on the power adapter, and find that the battery is shot, there is little chance of portable use anymore.

The battery is dead and cannot be recharged. Replace the battery.

How old is the tablet, it sound like the battery is faulty and not charging.