Re-installing the game will replace the game files located in Program Files...however, the game also stores data in AppData, an area that is not "cleaned out" by re-installing the game...

I am not familiar with Requim so I don't know if you have to manually place the mod or if it comes with an installer that puts it in the right place for you...if you had to place the mod manually in the mods folder, then you already know where to go to find all Sins related data in AppData....just delete all of that, and that might solve your problem...

If you don't know what I'm talking about, then first make sure you can view "hidden" files/folders...on windows 7 (and vista IIRC) you can click the "Organize" tab in the top left corner of any windows explorer, go to "Folder and search options", click the "View" tab, and then select "Show hidden files, folders, and drives" (should be a toggle somewhere in the middle of the list)...

Then, you need to proceed to C:\\Users\[Your Username]\AppData\Local\Ironclad Games\Sins of a Solar Empire

[Your Username] is simply whatever user installed the game (so probably you)...you can delete everything in that folder, and hopefully that will solve your problem...as a side note, this is where settings and mods are stored...you can actually find the settings file here and save it so you don't have to redo all your key bindings and the like when you reinstall the game...however, if you are having problems then I'd just delete everything there to save yourself some time instead of trying to figure out which file there is the problem...

Hope this helps...

You aren't trying to load a multiplayer game are you?  Like, load a saved multiplayer game...you're just trying to start new games right?  Also, you said original....does that mean original sins (like not entrenchment or diplomacy) or does that mean vanilla (no mods)?

So, you can't even start an MP game?  You aren't getting the "Disconnected from server" message are you?  Also, is this ICO or LAN?

Well here's my first shot in the dark...by chance, did you make the mouse click a hotkey to something?  Clearing out the AppData (and therefore the settings file) should have gotten rid of that...

Are you using a wireless mouse?  And if so, bluetooth or USB?  

Also, at the very least you can edit the settings file in AppData to change the "default" game settings (like game speed, pirates on/off, quickstart, etc...) so you can at least play a game with the settings you want (maybe you've already done this though)...