I remember having made some changes in Windows/system32 andsysWOW64 where I changed the file extension of the file"ExplorerFramae.dll to BAK" in both the folders and also copied theold file "ExplorerFrame.dll" as before,in bothe folders which was doefollowing instructions on net which became necessary as I could start Starttab,Search option tab,Microsoft Edge and almost all the links to other programson task bar including internet and for most of these when clicked to open theerror www popped up showing Explorer.exe in the upper line and" class notregistered." in the middle part.So,nutshell because of these issues I hadto look for a solution which after trying a few I got attracted by changing offile extensions (as stated above) from dll to BAK but also replacing dll fileextension in both the holders.
After doing this change the PC is not booting/ going further then log in frame but when log in it just go to a black screen with result that I can boot/login.

Shall appreciate any help to fix this situation