Before you all start yelling at me to go to the wiki, I already have. Many, many times.
On my old computer, I had tons of CC and mods for TS3 and TS4. I know how to install it already. I got a new computer and did all of the things you do to install mods and CC, but it isn't working in either game. (files that download directly into TS3 launcher are working, but none of the .package files are) I think it might be my computer and not me installing it wrong. I know it's not a lot to go on, but anything will help! Thanks.

have you enabled them in the sims 4 game options? Just asking the obvious question......

I've got custom content and script mods enabled

Sims 3 launcher won't install sims 4 mods and cc into the sims 4. Where are you putting the mods? My Documents/Electronic Arts/Sims 4/Mods
If that's where you are placing them, then I don't know why they are not working....

If your game is a pirated version then you have no hope getting mods to work.

nope, not pirated. as i said before, i had tons of cc for both ts3 and ts4 on my old computer so i know exactly how to install it. i think it may be my computer that's the problem, and i was hoping someone had had this happen before and could explain it. thanks though!

How many sub-folders deep are you into the mods folder? Your game can only read so far into the mods folder without modifying the resource.cfg file. Try downloading the No Intro mod (or another obvious mod you can quickly check), place it in "My Documents/Electronic Arts/Sims 4/Mods/NoIntro.package" rather than ".../Sims 4/Mods/Packages/Game/Removal Mods/NoIntro.package" for example.

The only other thing I can think of is that your game doesn't have the correct read permissions. Make sure you're playing the game from an admin account and check each folder to ensure you have read permissions. Not sure exactly how to solve this if it is the problem, but it might help you narrow down the issue.

It says they all have read permission when I check the folder properties, is that where I should be checking? Is there a way to check if I am playing from an admin account? (sorry if they're silly questions, I know nothing about computers)