What you see on the pic is neighborhood deco in Riverblossom Hills. I downloaded a cute no cc country home on MTS (the one with the red roof). I placed it, went to delete 90% of furniture and other things that inflate its price and when I saved and exited, everything was gone including the Riverblossom Hills's welcome picture. I exited the game, removed the neighborhood file and put it in again and got the same result. Before removing it, I checked the file and everything looked okay, nothing was deleted. I do have a backup but it's a bit behind, about a month or two behind. What could've made this happen and is it possible to fix it?

Are the lots gone from the Documents\EA Games\The Sims 2\Neighborhoods\Xxxx\Lots folder too? Do you have antivirus set to scan your Documents folder on access, or do you have One Drive/ cloud storage synching your Documents folder?

No, apparently the sims and the lots are there, I can open them on my SimPE but all of the memories are wiped. I just saw that I'm running very low on memory. I was careful but I'm not the only one using this computer. I did have some viruses and I deleted them, but they weren't in the sims file.

Running low on hard drive space can do this. It's something to keep a check on and keep a backup of your game always.

Just to check, did you actually mean memory, are you talking about hard drive space? Because, as Jo mentions, loss of data can occur when the game doesn't have enough writable space. If that has happened, your only real option is to restore a backup if you have one, or start over if you don't (as there will be lost data from this neighbourhood that you won't be able to repair). You may be able to salvage the hood terrain and some of the sims' appearance by cloning them to use in a new hood.
If you are talking about memory, then that's a different thing, although from your images it does look as though you have actual data missing.

Ohh, well damn. What would happen if I move Characters from my Neigborhood folder into a different Neigh folder?

You'll corrupt the new Neighbourhood.

You might just want to completely abandon this neighborhood until you get more memory and clean up your hard drive. It sounds like between hard drive space, memory and possible actual data corruption of the game, you cannot run the game properly.

Thanks guys and sorry for the late reply. I'm building a new custom neighborhood from scratch (except for lots downloaded from the internet). I'll try to fix my own laptop (it has battery issues and freezes whenever it's hyperventilating) and not having to share the simming laptop with my family.