One day, not long ago, my Steam wouldnt start anymore and I thought I just needed to restart my PC. After 5 times of restarting and trying to open Steam, I searched for help. I tried many things, and at the end I tried to delete Steam. I deleted about half of the files, because most of them were running in the background. I didnt know that before just now, so I couldnt delete Steam, open it or anything else. And I cant even find steamclientbootstrapper. I cant find it in the task manager or anywhere. I cant delete Steam since my Steam starts up when my PC does, and then I cant download steam again from Steam setup because Steam is already running in the background. And I cant stop Steam from running...
Start your PC in Safe Mode, then proceed to uninstall Steam from the Control Panel (Add/Remove Program).
What do you mean by deleted? I hope you mean uninstall and you didn't just try to delete the actual Steam files. Trying to delete the files directly (for any program) will usually not work for a multitude of reasons, one reason being that when you install programs registry entries will be installed as well which also need to be deleted, so unless you go through and delete all these as well you won't have a clean uninstall. Another reason, which is what you're experiencing is that things like Steam have background processes and services running which will prevent deletion as you found out.
If you tried to delete it try to uninstall it from Add/Remove Programs instead. Doing it this way will usually close all the services that are running and would prevent deletion.
Manual Registry Deletion
Note that messing with your registry can cause issues with your computer if you do not know what you are doing and make a mistake. I recommend that you export the entire registry as a backup that you can restore just in case.
Go to Run and type in
For 32 bit OS go to
HKEY_LOCAL_MACHINE\SOFTWARE\Valve\. Right-click on Valve and select Delete.
For 64-bit operating systems go to
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Valve\. Right-click on Valve and select Delete.
Then for both go to
HKEY_CURRENT_USER\Software\Valve\Steam Right-Click on Valve and select Delete.
Note you can stop it from starting up by running
msconfig and then try to turn everything Steam related to disabled (in services and startup (moved to task manager on 8) tab). This will allow you to delete the files after restarting as Steam won't be running. But I don't recommend just deleting files, always use the uninstaller provided as deleting files manually won't completely uninstall Steam (the registry entries and files in other locations issue that I mentioned previously).