RE: RF 5.5 crashes
Application software as a rule CAN NOT cause your computer to crash no matter what anyone may tell you to the contrary.
If there is a bug in the application software, such as Realflight, etc... the end result is that the operating system protects itself from the error and causes a return to the desktop... often abbreviated as a "CTD" ( Crash to Desktop ).
The application software works by making calls to API's and in turn the operating system to get the machine to render, produce sound, etc. via drivers.
Since the drivers have control of the actual hardware, an errant driver, or a driver that cannot handle an erroneous invocation properly, WILL cause the machine to freeze up or crash.
Give your description, it sounds like you have a hardware ( Heat ) or driver problem.
I'd suspect the latter first, but it could be either or both... Use an air blower to get rid of any dust bunnies and check the fans to see that they all spin. Also make sure that there is at least 2" or more all around the machine for cooling and that the area does not get warm or hot.
Some Windows Updates can replace library files that driver software relies upon causing problems...
Try downloading the latest drivers you can find for your motherboard, chipset, audio and video cards.
Then install each, rebooting after all have been installed.
Re-install Microsoft's DirectX9.0c redistributable ( yes even if you have a later operating system... that uses DX10 or DX11 ), then reboot again.
Finally reset Realflight to it's defaults via the launcher and try again.