A dllhost.exe is one of some most required vital part of Windows background process, it's COM+ hosting process controls processes in Internet Information Services (IIS) and it is used by many programs. For example, it loads the .NET runtime. There can be multiple instances of the DLLhost.exe process running in the same time. Defaulty, dllhost.exe is located in the folder C:\Windows\System32. Do not ever terminate or delete it.
If you accidentally removed it, you can copy dllhost.exe from another computer which has same version of Windows by using flash disk (or download dllhost.exe from internet and copy it into flashdisk, but it's not perfectly safe since certain websites give fake or infected dllhost.exe). Turn on your broken computer, and make sure that it is going to DOS or CMD mode on the black screen (since the computer is failed to open Windows welcome screen) or manually press particular button, usually F2 or F11 (try this if your broken computer can't open DOS or CMD mode, certain computers have different button to press).
When you have your broken computer on its DOS or CMD mode, insert the flash disk which has dllhost.exe copy inside. Use these command:
C> copy [drive]:\oldDirectory\ [drive]:\newDirectory\
Assume if your computer detects every USB in drive G, then you have to write this code:
C> copy G:\dllhost.exe C:\Windows\System32\
If you don't know where USB drive is, you have to remember how much drive partition in your drive and how much hardware in your computer. Usually, if you have 3 drive partition data and one CD/DVD reader, then the USB drive would be at G (it is counted from 3 drive partition; C, D, E and one CD/DVD as hardware; F).
Then, the computer will copy dllhost.exe, after this just do restart your broken computer and it will get the Windows welcome screen back and you will able to enter it as well.
But it is recommended to reinstall your Windows, this trick is only purposed if want to rescue your important files and copy them to flash disk.