You probably got a defective phone. Where did you get your S710a, anyway?...eBay, probably?
You should try doing the usual troubleshooting
- turn off, take out battery, put battery back in after 1min
- take battery off while unit is still on, put battery back in
- master reset
- for internet settings, go to SE website and SMS them to your phone
- update firmware through SEUS
- flash phone's firmware
If the problem still persists, then you have a hardware problem. It might be just the antenna since you said that you are not receiving/making any calls. Just have it replaced by either taking it to a cell phone repair shop, or doing it yourself. If it is the main board, it might have likely been damaged in some way. If you got it from eBay used, the phone might have been dropped, or the seller changed the housing to make it look new and accidentally damaged part of the phone, or something else entirely...it might be water damage. More than likely you're not going to ship it to SE for repair, because repairs can cost at least $100 if there is no warranty. Probably the best thing is look for a local cell phone repair shop and let them diagnose it. Or sell it for parts, then use the difference to buy another S710a. Or you can take the phone apart yourself, get another S710a main board from a parts phone, and switch them. Just remember, if you're not used to taking phones apart, always be patient and remember where everything goes because the S710a is a bit more complicated than others. If you're not comfortable with that, find someone who can help you in your local area.