(See the best response by Shadowkaroth.)
BYOND won't open,
what should I do?
Best response
Please elaborate with a little bit more information...

BYOND as in the Pager won't boot up for you to login at all?

Games won't popup/give an ad?

Try using the Pager to connect to the games you are having an issue with. I'm not sure how the BYOND:// protocol works but it may be experiencing issues on your system preventing you from getting the popup to outbound connect to a byond://