Okay, fixed it! I don't know if this will help anybody but this is what I did.
Within my wwwroot directory, I was told in a tutorial to edit a web.config file or something. What I did was completely delete all files (even that webconfig file) within the wwwroot dir expect the .net asp folder.
I download wordpress and moved fresh copy to the root dir. went into the PHPMYADMIN and dropped the wordpress db for old one. started a new db with new name. edited the wp-config file with proper names.
Installed wordpress and worked! Uploaded my old theme, (which I honestly never tested before) and 500 ERROR!
The ERROR (for me) was my theme! 2 .php files got corrupt somehow. Check you current theme! The blank screen solution is something to do with your browser or the network your on. My site works, but shows up blank when im at work (due to my works network).
SO BLANK is network or browser problem - 500 error could be your theme. Delete your theme and use the default and see if that helps! CODE NEVER CHANGES, ITS CODE! IF IT WORKED BEFORE THEN A FILE SOMEHOW GOT CORRUPT!