Open the IIS control panel and head into PHP manager, then go to error reporting and enable development mode (off the top of my head) and it should tell you what's wrong.
I would enjoy staying on a forum that has a welcoming and friendly community, and also has a wide range of topics to offer. There should be something there to keep people interested and involved too.
Are you using a different cracked version at all? If it's different to the version you had before everything went down then you might have some database issues.
Windows 7. I upgraded to Windows 8 however I didn't really get used to the whole Metro thing, I might go back at some point but I doubt it. Windows 7 has always worked like a charm for me.