Computer used to run League at 300 max settings, but after mobo repair it onlys at 30 even at lowest

Hey all, I know I should just contact Dell support but I'm sick of using support for anything basically every week, so I was wondering if anyone has ever had the same issue as I have had

Heres the rundown:

While I was gone apparently my mobo (MotherBoard) was fried, so we shipped it to Dell and they replaced it. We get it back about a week later and the first thing we do is reinstall the drives, uninstalled a lot of unimportant things, and then gave it a few days to do nothing before I loaded onto league two days later. I noticed even the client was super laggy even though it used to run smooth (I played it off cuz then client sux lmao) and once I got into champ select it was even slower. Of course I was weirded out but I just assumed it was being dumb since we just got it back. Once I got in game, I noticed my fps was a constant 25-30. Framerate was uncapped and on the highest setting as usual. I used to get 354 on average and now its been a whole week and I only have gotten 20-40 every time I play. I tried setting my NVIDIA to perform at maximum performance but it only runs at 40%

The computer I use is the Dell XPS 8910 it has- 16 gb ram Nvidia 750TI Intel core I7-6700 cpu @ 3.40 GHz

Please help its giving me the days of when I used a 300$ laptop all over again D: