Welcome ,I will give a full and clear answer to your question, please make sure to reply to any questions I have. They may be essential to my reply.
Hi sounds like its stuck in recovery mode.
3g or 3gs ?
3gs has chrome writing on the rear .
Is , was the phone jail broke ?
What version of ios was installed ?
You will need some software to make changes to the iphone .
You need to down grade the firmware to : iPhone (3.1.3 or 3.1.2)
Here's where to get the firmware :
You will need Java installed on your PC if not already :
Plug the iphone in to the USB of computer , quit iTunes .
Click on connected devices .
Then press , start TSS server .
Then open iTunes .
Then click on your iphone in iTunes .
Then Hold shift key on your computer keyboard , & click restore
If the phone was already syncing slide to stop it before the last step ..
A window will pop up , to look for the firmware you downloaded . , "iphone, 1,2_ etc . restore file . click open on the file .
Tinyumbrella must be running .
Please wait .
iTunes should then say extracting software .
Then preparing iphone restore should display , and wait . .
It will take a few mins at least from here . .
iTunes will say restoring iPhone software .
Make sure you have a good USB cable and don't disturb it while this is working .
The progress bar in iTunes should be moving along .
Dont touch anything while its working .
You may get an error 1015 at the end of the restore , this is normal as its downgrading . .
The iPhone should have a Progress bar on it moving slowly as its working .
After the error 1015 , click ok .
iTunes may pop up more error info , click ok .
Then quit itunes .
The phone will be in recovery mode .
Now go to , Tinyumbrella and click stop TSS server .
Then go recovery devices in Tinyumbrella click iPhone , and then press the exit recovery button to the right .
The iPhone should power off and on again ,
Leave it plugged in .
The apple logo should come on screen , with a progress bar .
Once powered on , install your sim card .
And then unplug the USB cable .
Now plug the USB cable back in .
The phone should activate , and be downgraded to the Firmware version used .
I hope this helps.