Forgive me if I state the obvious but I find it best to start with the basics then work on from there.
First battery out wait 30 seconds battery back in - retest Can you surf the web ( this is checking data connection ) IF yes are you on WiFi or GPRs ( the mobile data network ) If unable to surf web then you have no data connection or the WiFi log on had failed or the mobile APN is messing - or mobile data is turned off - all things to check. ( If no data on wifi turn it off and try gprs and vice versa ) Go into your email account [menu] try refresh now If you have more than one email account it is unlikely that they would all stop at the same time If you have only one email address - delete and re add If all of the above fails then look for a software update for your handset
If you could tell us what you see on the top of the screen ( wifi symbol or GPRS symbol either G H E or 3G that would help. Also your mobile service provider and then we could look up the APN settings you need.