It doesn't open and doesn't charge how can I fix this problem?

Checking the battery is a good place to start, If it's been sitting unused for a long time before this happened it's even more likely to be the cause, the battery voltage might have dropped too low for the tablet to accept a charge. To confirm this you would need to pop open the tablet and check the battery voltage with a multimeter. If the battery voltage is lower than 3v or there is no voltage at all, then the battery is bad. Depending on your skill level, you could either try to charge the battery back up using a bench power supply enough to get it to charge again, buy a replacement battery and change the battery or take it to a shop to replace the battery. Always be careful when working with batteries as it can be risky, if you are not experienced go ahead and replace it, don't try to charge it with an external power supply.