I can't use steam D:

when ever I start up my computer (or steam) I get this. . . I tried retstarting steam, I’ve tried rebooting, and I uninstalled then re installed

maybe that file was deleted have checked to see if it was there?

This is a steam issue, not a Gmod issue. I suggest asking on the steam support site for more help…

Check this:
Crash: Steam.exe (main exception): Unable to load library Steam.dll

DrumStick, if Steam’s files get deleted it redownloads them, using the same system as if you delete HL2 manually.

Delete Steam.DLL and start steam, it should redownload and fix whatever was wrong.