I had this problem in Eclipse today so hopefully this helps out.
If you go to Tools - Java Platforms, what does it show? It should show your current Java JDK. If not:
1) Verify that you have a JDK installed under C:\Program Files\Java\ or C:\Program Files (x86)
2) If so, select Add Platform and add the JDK folder (e.g. jdk1.8.0_25) back to your platform list
3) If not, re-download and install the JDK and do step 2
Also, you should be able to right click on your Java Project, go to Libraries, and see the current JDK (Java Platform) that is being used.
javaandjavacfrom cmd, could that have done it?