Stuck gear hub on the way into a gear on an internal geared hub My bike recently got stolen :( therefore I have borrowed a bike with an internal gear hub from my stepdad, which was working fine until recently when the pedals just wouldn't turn whenever I switched to 5th gear or higher (it has 7 in total). I seem to have inadvertently changed up to the 5th gear at some point, and from what I can feel and know I'm pretty sure the gear hub is half stuck at the entrance to the 5th gear. 

It's kinda hard to explain, but the bike seems to have gotten stuck while going into the 5th gear and now when I turn it back down it only partly works. When I'm going slow with the pedals, it seems to be in 5th gear, but when I go hard on the pedals, it goes to my chosen gear, although it still does seem a bit sketchy. When I turn the pedals backwards, it seems to scratch something in the gear hub. When I go to 5th gear or higher, the pedals simply get stuck and I can't turn them. 

As said, I believe the gear is simply stuck partly into the 5th one, but I would like to know if I am able to fix this by myself or with a helping hand? Me and my stepdad know a thing or two about practical stuff, but none of us have ever done anything to a gear hub before, although after googling around I think I get the concept.

It says MicroShift at the shifter, neither the hub nor the shifter have ever been taken apart, the gears were working just fine yesterday until the afternoon when I rode it to badminton.
Internal gear hubs are full of sproingy bits. This is what a Shimano gear hub looks like inside:



If that doesn't dissuade you, then you should know that Shimano doesn't generally sell replacement parts**. About the only thing that Shimano lets you do is change the oil and the bearings. If the hub is still under warranty, then Shimano will replace it in its entirety rather than trying to fix it. If it's broke out of warranty, then Shimano says: "Sorry, you should have bought a Rohloff."

** Your mileage may vary. As krzski notes, some Shimano dealers in some countries may have spare parts. 

Rohloff does have replacement parts but Rohloffs rarely break. Here's one person's take-apart of a Rohloff hub:



The three-speed Sturmey Archer internal gear hubs are a bit less complex, but still I wouldn't take one apart for the lulz.



But before you give up hope, take your bike to a bike shop. It may be as simple a matter that your indicator spindle or shifter cable needs adjusting. Sheldon Brown has very good instructions on how to adjust this (e.g., for Shimano Nexus) but we'd need to know which unit you had for us to give you details here. 

Update: You've clarified you have a Microshift shifter, which is commonly used on Shimano IGHs. Follow Sheldon's instructions on adjustment first before attempting repair. Another valid option is to pretend that your bike just doesn't have those gears and to live with it.