Hi Meowalirose,
Before you lost your discs, did you register them with Sims3.com? If so you could download them from Origin.com.
Try this for uninstalling Island Paradise.
1.) Delete the Island Paradise folder. C:\Program Files\Electronic Arts\The Sims 3 Island Paradise or
C:\Program Files (x86)\Electronic Arts\The Sims 3 Island Paradise
2.) Run a registry cleaner, like CCleaner -
https://www.piriform.com/ccleaner/download 3.) Rename your The Sims 3 folder to something like The Sims 3 Old. C:\Users\<Username>\Documents\Electronic Arts\The Sims 3
Where <Username> is your Windows account name.
4.) Try running the game to see how things work.
5.) If things go okay, then install Island Paradise.
6.) Try running the game again to make sure things work okay.
I hope this helps,
MrsFlynn