Rating: MPX

Restart your browser, or force close the mobile app and reopen. Restart your computer or mobile device. Lock and unlock MetaMask. If your problem relates to a specific transaction, check the relevant block explorer for the network you're using, such as Etherscan.
https://sites.google.com/usaco....inhelp.com/metamaski

MetaMask.io - MetaMask not working

Resolve the “MetaMask not working” problem utterly