Hi Ele,
We recently reinstalled Sims 3 on Hubby's computer using the disc version and didn't run into any problems with Origin. I did let him know of your post to see if he might be able to help.
Installing Sims 3 shouldn't interfere with Sims 1 or 2.
You may want to try running a register cleaner program. (Something like Ccleaner -
http://www.piriform.com/ccleaner/download) This helps clean up temporary files, internet cache files and other files that are left behind that are no longer being used.
Also maybe try disk cleanup and defrag. As they maybe helpful to do as well.
Disk Cleanup and Defrag are helpful to do as well.
-- All Programs > Accessories > System Tools > Disk Clean Up
-- All Programs > Accessories > System Tools > Defragmenter
Restart your computer and then start reinstalling your Expansions and Stuff packs, let the installer patch as you go. Start with The Sims 3 Base Game and go from there.
Hope this helps,
MrsFlynn