Have you tried dfu mode? If you tried recovery mode that usually works but if it doesn't you may want to try to connect the iphone to the computer hold down the home and sleep/wake button for exactly ten seconds. After 10 seconds release the sleep wake button but continue to hold the home button. This is putting the device into dfu mode. The screen should be black. It may take a few attempts to get your iPhone into DFU mode. Generally, hold down both buttons then release the Home button just before you think the Apple logo would appear. If you are still holding both buttons down and you see the Apple logo you are holding them down for too long!
Typically, when the ios upgrades the developers of the apps are forced to upgrade their app software to be compatible with the newest version. So you won't find any apps in the app store that are compatible with ios 4.3 You can check what software the app needs in the app store under the picture of the app and the price It will say category and under that will be a title that says requirements. That will tell you if any apps are compatible with your iphone. Most likely you will not find any. It doesn't mean you don't have a good iphone though. It's still a great mp3 player and camera as well as a decent internet surfing device. If you're fine without the apps you can still enjoy it.