When you install make sure you have the ESF folder in one of two directories.
STEAM C
rogram Files\Steam\Steamapps\Emailaddress\Half-life\Esf
WON C:Sierra\Half-Life\Esf
Make sure your Half-Life folder (The one before ESF) has a file called Fmod.dll in it.
If it does, make sure it's up to date. Then go into ESF, Make sure you have a file called "client.dll" in your Cl_dlls folder (cl_dlls\client.dll) and check the Dll folder for hl.dll
(dll\hl.dll). If you still have problems post again.