Windows 10 -- ALT Tab low FPS until restart.

[ItzJustMM]

Hey, so basically a friend of mine gave me Windows 10, in which I installed it.
When I'm playing Fortnite on 1920x1080 at low graphics (View distance Epic) I alt tab as Iget a steam message, as soon as I tab back in it drops down to 20 fps. To fix this, it happens on any game. I have to restart my computer to fix it, which is annoying because I have to keep logging back in
Any help would be appreciated.
PC Spec -
AMD A8 6600K @ OC 4.1GHz
GIGABYTE F2A88XM-DS2
NVIDIA GeForce GTX 550 Ti 2GB
8192MB DDR3 RAM 1600MHZ
Drevo X1 Pro SSD

 

[Mattp2017]

Try disabling the steam overlay..... Right click on the game in your steam library then go to properties, under the general tab, uncheck the box that says enable the steam overlay while in game.