Believe me when I say, this is one of the most frustrating things to happen!
Imagine this, I first get into Crypto - I buy 5 Ether through coinbase - download the Ethereum Wallet so I can have an offline Wallet store and without thinking about it - I got the wallet address and sent it all.
I then left my i7, 12GB, 1TB SSD Linux machine running with QoS enabled for bandwidth benefits for three days.. gradually getting more and more nervous.
I couldn't seem to get past the last few blocks, it would stall or just never really get anywhere!
Firstly, as an observation - I found that if you launch the application - you lose any form of syncing entirely, so leave it at the splash screen.
Secondly however if you really don't think its going to connect, then try these steps:
Go to the Develop Menu item, and change your Sync mode to "Light" it may say Beta on it but its ok.
Go to File > Backup > Accounts data
Rename ChainData to ChainData1 (or whatever you want). Close down your Wallet and re-launch it.
This didn't work first time for me, (maybe I was too keen) but if thats the case - have faith, close the app again and re-open it. Leave it on Splash, give it 15 minutes (or so depending on your circumstance) and horrar it should work!!!
Hope this helps somebody else who may have stupidly jumped without looking too...
If this post helped you, please consider donating eth (every little helps!) to my addresses on the right of this page!