Windows / MacOS compatibly

I’ve only gotten a PC few days ago, and I realised I wasnt able to open the documents on the Windows system. I tried to export it as a Scrivener 2 document, it still won’t open.
I tried to download Scrivener 2 on mac, it won’t allow me to run it.
I am using dropbox as the sync system.
If anyone can provide anything to help would be great, thanks.

A little more info please. What version are you running on the Win machine, and am I correct in thinking you have V3 on Mac.