Re: Cannot open Exployer. exe
Try doin a system restore. Might be that can help... nothing else as seems you have tried the basic steps... Try system restore by browsing from task manager!!
Re: Cannot open Explorer.exe
Have you tried safe mode? Can you run eventvwr as a task? This might give an indication of what is not loading properly.
Also click on start up... File corruption causes explorer not to load?
If you fell it like hard drive issue, you can download the relevant tools from the drive manufacturer's website and run a full scan on your disk to see what's going on.