We have seen this occur because of two issues. First, there can be an Internet Explorer setting that causes this. There is some security setting on IE that doesn't allow other programs to enter values and submit data. We believe it's one of the settings in the Scripting area (see screen shots below). You can try disabling all of those values, logging into Tube Toolbox and see what happens.
If that does not work, the other thing you should try is to download and re-install Internet Explorer - http://www.microsoft.com/windows/internet-explorer/worldwide-sites.aspx
Note: It does not matter if you are using a different browser as Tube Toolbox uses Internet Explorer for all its browsing. After installing Internet Explorer you can try Tube Toolbox again.