It won't load Sims? My other games are all there but the game icon thingies that you click on to run the game, the 'Sims 2' one has been replaced by a dark grey tile with 'Origin' written in it. Earlier it did load the game when I clicked on that tile long enough but now nothing's happening at all. Is this an issue everyone's having or just me?

You can just run the game from the Icon on the Desktop - no need to get Origin up and running for TS2 - maybe try that? If there's still a problem, you will need to load Origin, right-click on the TS2 icon and see if there's an option to repair the game (be warned this may reset the game - if you want to keep CC and neighbourhoods, make a back up first).

Origin may just be updating or offline or something - they tend to do that at times. If the OP uses UC, then a desktop icon may not be present, because the player has to make one.
Go to C:/Program Files (x86)/Origin Games/The Sims 2 Ultimate Collection/Fun with Pets/SP9/TSBin
Right-click on Sims2SP9.exe and click Create Shortcut
Drag the shortcut to your desktop, or wherever you want it, and rename it if you like. This shortcut will open the game without opening Origin

For some reason that I just don't get, running the game through the desktop icon is no use - it doesn't load my downloads or custom neighborhoods that way!