DYI Stud Finder

The stud finders are not expensive but you can sometimes use a magnet to find the nails. Also you might try shining a flashlight across the wall. The putty put over the nails will sometimes show up. Last resort is to tap on the wall and try and hear the areas that have support under them.

It's probably broken.You can buy a new stud finder.

In order to support any true weight (like books) you will need to use wood blocking between the metal studs. Measure space between the studs, cut blocks to fit and mount at location where brackets will be.

For lighter weight applications, you can use an expansion anchor (but not the cheep little plastic ones that are often provided). A common name for this anchor would be a "molly anchor" and they are available at all hardware stores in a variety of capacities.

http://www.lowes.com/lowes/lkn?action=productDetail&productId=230779-37672-376056&lpage=none

That's because of corrosion. It happens!

The broken studs have to be cut, or ground down flush, with the thermostat housing. Then a center punch is used to make a deep dimple, in the center of the broken stud.

Next use a small drill bit to make a pilot hole.
Two times smaller than the stud. (Bolt)
Use caution, as you don't want the drill bit to walk off to one side. Keep the drill level, and vertical.

Now come back with a larger drill bit, but one that is smaller than the stud/bolt, and will stay away from the threads. Try to drill at least one-half inch in depth. Use an Easy Out, bolt extractor.

If it feels as though the Easy Out bolt extractor, is being forced too much, and you think there is a possibility of it breaking, STOP!
Use a drill bit that is large enough, to drill a hole that will not touch the threads. Then work a small chisel along the outside edges of the bolt 'Shell', and work that thin shell to the inside. Use a pair of needle nose pliers to try to extract the shell out. One piece at a time.

(After you have drilled the center of a stud, or bolt, out to where the threads are, there is a thin metal shell left behind)