This system hanging is a confirmed windows problem due to a recent update that Microsoft pushed.
Same prob here, and another user
http://forum.tixati.com/support/2037/
It happens more when Tixati is running because it makes heavier use of network/disk resources than other programs like web browser etc.
Microsoft will fix this soon and push an update lets hope. This is definitely NOT the first time this has happened. Early days of Windows 7 had all sorts of crazy stuff come and go.