@kareen2016 to charge your tablet you will have to use the AC adapter, not the USB cable. If your tablet does not connect to your computer with a charged battery, check your settings first.
To change your tablet’s USB connection options, you should go to Settings >DEVICE > Storage, and tap Menu icon at the upper right corner. Then tap USB computer connection to enter to setup.
If it still does not connect, try a different cable as well as a different USB port on your computer. Should this still fail, you will have to disassemble it using [https://www.ifixit.com/GuideRCA+RCT6272W23+Motherboard+Replacement/39533|this guide]. check the USB post to make sure that it is still properly attached to the motherboard. If it is, repalce it with a new one. If it is not, solder it back on. Remember to charge your battery first. The tablet will not get recognized with an empty battery.