Computer Goes Back To A Certain Point Every Time Log In?

so everytime I log-in to my computer it basically restores back to a certian point.And also It starts as a black screen with nothing except for my mouse until I open Task manager and run explorer.exe which for some reason doesnt run on its own anymore. Its probably due to the fact that I wanted to put a cool theme on my computer and that involves replacing the explorer.exe file and explorerframe.dll file, and I did that. But then I decided I didn't need a theme so I put the original Explorer.exe and explorerframe.dll back on to replace the ones I put on before. It changed everything back to normal except for the start orb. I wanted the old start back or atleast a new one. So I got windows Start orb changer. It worked well for some time until at one point everytime I turned on my computer I got an error saying expstart.exe failed and something about bitmaps. and It just black screens until I run explorer.exe from the task manager...and goes back a day or so