addnodes aren't needed.
have you tried disabling your firewall? Usually you can right click it (comodo, avast, etc) and select "disable for: 15 minutes".
Disable your firewall and see if it connects.
If not, you may be using an old wallet?
The new wallets are designed not to communicate with the old ones, for security purposes.
You won't be able to sync if you are using 0.7.5 or lower.
Try redownloading the wallet. Works fine for everyone else so that only leaves an issue on your end.
If you want some help troubleshooting you can find me on the IRC or send me a PM.