It's important to know what is XXXX.
Normally, if XXXX is a time. Like i can't get the computer to work before eight o'clock. Then the first sentence is better and it would be unreasonable to add ' , '.
If the second sentence is used, the thing after 'before' should be a sentence.
For example: i can't get the computer to work, before you hit me can you check what is the problem with it?