I cleared the cache of my GMail application and now I am not able to use it. How can I fix it?
Most probably you have turned on two step verification just turn it off or make an application specific password and try with it
What kind of phone?
Are you able to connect to GMail via the browser on your mobile? If not, you may not have data active on your phone right now. Otherwise, I agree with the above that you may have two step authentication set up on your GMail account, which you can switch off temporarily.
Two steps verification