Data problem

Unfortunately there is more than one possible explanation for that:

* Handset settings: are your Access Point Names (APN) settings correct (will be in your mobile data settings - correct values depend on your service provider, you should be able to find them with a web search)

* SIM fault: if it's this the only fix is to contact your provider for a new SIM

* Service problem: a fault with your local basestation or a problem with your account settings. If the problem is the same wherever you are (assuming you are moving around - many are not at the moment) then it's not a local issue, but there can be issues specific to your account or to certain groups of accounts. For anything like this you need to speak to your service provider.

If you have access to another handset try swapping the SIM into it. If you have the same problem then it's not your phone, but it could still be the SIM, your account or a network issue. Have you had any other symptoms or oddities?

I'm also making a couple of assumptions here: I'm assuming that you've done obvious things like rebooting the phone (you could also try removing the SIM and re-inserting it, maybe even cleaning the contacts with a pencil eraser). I'm also assuming that you've not made any modifications to the system software (e.g. flashing custom ROMs, RILs or similar). If the first assumption is wrong then try that, if the second is wrong then let us know what you have done.

I'm also assuming that you've had the phone for some time, as it's an old phone. If you've just acquired it and it has never worked for you, or you've changed provider and it no longer works, then again please let us know, as that changes the picture too.

have you talked to your service provider? it might be on their end and not yours. so if @Hadron's suggestions do not work, i would contact your service provider and see if they can figure out what is going on.