This applies to your issues:
Found in: MasterCores -Download support.
So it's time to play the game "what's blocking the client?", which is kind off a hide and seek game.
I'd start with disable antivirus/firewall for a few minutes, to see if that would make the client start properly, If so.. you only need to figure out how to whitelist the client so it's not blocked.
If it's not antivirus, it could be windows firewall, same there, inactivate to try out the client and so on..
If that wont help either, then try to relocate the client to another folder/harddrive, maybe the location the client is in have been locked for the tasks it's trying to do. (yeah, windows can get these orders by antiviruses to block folders etc).
Give it a few tries, and tell me how it went