Brought a fresh: DigistumpArduinoInstall1.5.8B.exe to a freshly built Win 8.1 PRO x64 machine I've ignored for 10 months [never installed Arduino or DigiStump drivers or anything].
DigiMouse example compiles, after selecting Pro

. And it works

, unplugging can leave the mouse in an ODD state, of course.
> Surprise? - No BLINK pre-load from factory (on my 4 PROs)? It boots to perpetual bootloader 'wait for upload'.
> My first USB2 port resulted in 'Flash write error -1' - so picked another USB2 and it worked. Just tried USB3 and the PRO uploaded!
> No included IDE DigiSpark blink example with pin1 set? Went to 01.Basics (edit 13 to 1) and all four now blink!
> When I chose default install path to Programs - it seemed default open sketch was "documents/Arduino", not "program files(x86)/Digistump_Arduino". This was a NEW user account and I had "documents\arduino\libraries" with a readme.txt in?
I uninstalled and re-installed and it then seemed to start in "documents\Digistump_Arduino" where installed
-Funny (Win) IDE thing: Open two sketches - compile 1st and switch to 2nd and the compile output after that goes to 2nd.
-Also saw updated MicrOledPRO with two examples! Didn't try that yet.