Please include the following:
Your OS and version: Windows 8.1 x64 (Including a dxdiag report also works. Also please specify if you are using Windows 8.0 or 8.1 and if it's 32 or 64 bit)
The version of RTST: 0.9.1.2
Description of the problem.
What you were doing last.
Including any logs.txt under the Real-Time Stat Tracker directory can also be really helpful. If you have Debug Log enabled in options there will be multiple log files.