iPhone 4S problem.. Someone please help

• Try a forced restart: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps BEFORE doing the restart.
• Try resetting you network settings (Settings app > General > Reset > Reset Network Settings (you will of course have to add the network back in.

Also, when you say "connected to the Net" what does that mean? Via WiFi? And if so, under what circumstances? Is this just at home? You might consider restarting your router or even checking for firmware updates for it.

KenC44 wrote:

So far I've only tested it in a home network (via Wi-Fi). The router (mine is actually a modem) is working just fine for other devices,which makes me thinking that it's not causing the trouble.

Actually, yes it could be. Restart it, and also check for a firmware update.

No, it appears you are already up to date on iOS. What I have suggested so far:

• Try a forced restart: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps BEFORE doing the restart.
• Try resetting you network settings (Settings app > General > Reset > Reset Network Settings (you will of course have to add the network back in.
• Update the firm ware on your Modem/Router (see the manufacturer's instruction or web site).

Have you tried any of these thus far?

So you have updated your router's firmware?

Have you tested on a different network?

The only remaining thing I can recommend is to restore the device as new: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support