See if your router IP has changed, if that is the case you will need to create a static IP. Go to www.portforward.com and find your router, there should be a part about making a static IP.

Btw if anyone wants to help me: I once had connection probs and fowarderd my ports, then the problem was over. A few months later my router IP changed, when I found that out I solved the problem again, then someday I had those problems again, nothing seems to work including making a static IP, I could host first and only some people were able to join my server, then I tryed some things with my router and now I cant host anymore. I have the 30 sec problem in most servers except in the Zeal Alpha server, where I mostly can join normally. Normally, because I can use the -connect option at properties with which I can join most (public) servers.

EDIT: My router is a Gigaset SX 552 WLAN dsl