Please contact me at mar@devl.org
I can probably help with the issue. A soldering problem is the most likely, although not if you've had it professionally done.
If you are confident that the soldering is good, then it could be a layout/hookup issue.
Another common problem is that the part isn't erased (and therefore you can't enter the bootloader). This often happens when you flash it incorrectly. Try to do an hardware erase (with the VREF pins and reset).
I can look over your schematic/hookup to find problems. I also have a variety of firmware tests that can help isolate the issue.
-Mar.
