I used to be able to download as much mods as i could but for some reason starting yesterday when i tried to download a mod, any mod a error window would pop up saying cannot open c/windows/system32/config/systemprofile/downloads.

I tried different mods, doesn't matter which mod that error box keeps poping out everytime i tried downloading a mod. I even uninstall winrar and than reinstall it and the same thing still happens. And i also can't click on data files in the morrowind launcher, everytime i click on it, morrowind stops working. If anyone know any solution to these two problems, please help. The second problem isn't that important since a simple reinstall can fix it i think. Thanks in advance.

I'm not saying this to scare you, but to me it sounds like a deeper problem than just "not able to mod Morrowind"

I'd scan that Hard drive for errors

What version of Windows are you running to have the system try to dowload to /windows/system32? But, yeah, like Rysty said you've got bigger problems than an inability to mod Morrowind.