I read and did all the steps in this thread and none worked. I too was having problem with Pl Sql developer.
Finally what worked was simple:
Step 1: Open your registry (Start --> Run --> regedit)
Step 2: [HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE]
Right click on ORACLE and click on New --> String Value
Enter the name as ORACLE_HOME. Double click that again and enter the Value data to your oracle home path which works fine.
Not sure if this is the place where I shud ask this qs...I am trying to install oracle 11g client in my comp (win 7-64 bit).It is not thorwing any error but the folders etc are not being created as well -where I can put my tns names and all.Even toad says no client s found..What shall i do?