The easiest way to fix this issue is to actually uninstall the application then use a registry cleaner to fix the obsolete entries. Since Bluestacks is still in beta mode, errors may appear from time to time. Remove Bluestacks, then install CCleaner to clean the registry, reboot the computer, download Bluestacks again and it will work normally this time.
Note: Bluestacks requires at least 2 GB RAM to be able to run properly. Try to upgrade your RAM memory.