Most likely the issue is that your computer time is not synchronized with the internet time. This is how to fix this:
On your Mac, choose Apple menu > System Preferences, then click Date & Time.
Click Date & Time, then set the date and time automatically.
Go to Start > Settings > Time & language > Date & time.
Then set time automatically.
Make sure you are connected with Metamask on the ETH mainnet.
Try with Chrome or Firefox browser.
To be able to vote you need voting power, your voting power is calculated at the "snapshot" of the proposal. The snapshot is the block number where the voting power matter, if you don't have any token at this block number you will not have any voting power and won't be able to vote.