I was having this problem (iphone 5 wouldn't work as hotspot for my PC laptop) and had tried everything suggested on these message boards, so I finally went to the Apple Genius Bar and they fixed it for me. Here's what they did:
1) Turned the Hotspot off on my iphone
2) Went to the Control Panel on my laptop to "Network and Internet" > "Network and Sharing Center" > "Manage Wireless Networks" (on the left navigation panel) and deleted my iphone from the list of WiFi connections I've attempted.
3) Flipped the manual WiFi switch on my laptop to Off and then back On again (to reset it)
4) Turned the Hotspot on my iphone back on
After that, when I tried to connect, it worked. Hope this works for someone else.