If you're absolutely sure you have 64-bit Java 7 installed, and it exists in C:\Program Files\Java\jre7, then try this file:
https://www.dropbox.com/s/nzjw3k8reus6sao/jre7x64.reg
That will create the registry entries that the FTB launcher looks for when searching for Java versions on your system.
If you do not have the folder I mentioned, I'd suggest as others have to try updating to Java 8.
i opened that file and installed regedit key after restart still max ram 1.5gb
JavaFinder.parseWinJavaVersion:137: Java Version: 1.7.0_45 sorted as: 1.7.0_45 32 Bit Java at : C:\Program Files\Java\jre7\bin\java.exe
[16:14:05] [INFO] JavaFinder.parseWinJavaVersion:137: Java Version: 1.7.0_45 sorted as: 1.7.0_45 32 Bit Java at : C:\Windows\system32\java.exe
[16:14:05] [INFO] JavaFinder.parseWinJavaVersion:164: FTB Launcher Prefers: Java Version: 1.7.0_45 sorted as: 1.7.0_45 32 Bit Java at : C:\Program Files\Java\jre7\bin\java.exe
Im gonna try java 8 but how about after uninstalling java delete this files ? Maybe they cant be deleted
EDIT:Before installing java8 i tried AforAnonymous's answer and didnt work again.
EDIT2:Omg i installed java8 and still max ram 1.5gb look at that log
[17:02:12] [INFO] JavaFinder.parseWinJavaVersion:137: Java Version: 1.8.0-ea sorted as: 1.8.0_0 32 Bit Java at : C:\Program Files\Java\jre8\bin\java.exe [17:02:12]
[INFO] JavaFinder.parseWinJavaVersion:137: Java Version: 1.8.0-ea sorted as: 1.8.0_0 32 Bit Java at : C:\Windows\system32\java.exe [17:02:12]
[INFO] JavaFinder.parseWinJavaVersion:164: FTB Launcher Prefers: Java Version: 1.8.0-ea sorted as: 1.8.0_0 32 Bit Java at : C:\Program Files\Java\jre8\bin\java.exe