I have found that the GUI wallet sticks from time to time and the only solution I have found has been to delete the GUI main folder (the one extracted from the zipped download. Don't delete the Neo file in Win app data/local) and re-install from a fresh download. It does mean syncing again and I have not yet found a "how to" for the bootstrap chain file which is available. It can be a pain sometimes using the GUI wallet especially as the NEON wallet is improving all the time. An easy to find bootstrap file with a guide would make life easier for those of us who like to use the GUI wallet.