Starting from MT4 Build 600+ onwards Metaquotes has changed metatrader files data structure and so there is a change in Installation of Custom MQL4 indicatorsAdvisors. The change happened majorly because Starting from Windows Vista onwards, Microsoft has introduced a restriction on writing to Program Files directory. And mostly programs are not allowed to store their data in Program Files folder if User Account Control (UAC System) is enabled.

So metaquotes placed all its files, expert advisors, indicators, templates , historical data outside the Program Files folder. Instead the files are placed inside the user data directory stored in a special place called terminal data folder.

 
Steps to Install Custom indicator to Metatrader 4 with Build 600+

1)Download the Custom mql4 indicator in your local computer.
2)Right Click over the mql4 indicator and copy it.
3)To Access the Terminal data folder Open Metatrader->Goto File Menu->Click on Open Data Folder

4)Open MQL4 Folder

5)Now Open Indicator Folder and Paste your mql4 file

6)Now close and Open your Metatrader. Under the Navigation Panel-> Custom Indicators folder to see the newly installed Indicator. Now drag and drop the indicator to the chart to start using it.