Hi, don't know if you figured it out or not:
You probably don't have your SD Card formatted exactly right to FAT 32.
That is what happened to me. I use a Mac, so you can't just right click and format the card. So I went into Disk Utility, and got the idea that what i would do was partition the SD Card, one side Mac OS one side Windows FAT 32. However, it won't do that. The partition itself reverts to FAT 16. So if you are using a Mac. Go into Disk Utility and chose to format the disk with whatever the generic Windows option is: just don't chose FAT 16. IT REALLY HAS TO BE FAT 32. I bet you get a flash like the thing is about to go, and then it stops. If you could see the words on the grey/blue screen, which I got it to do at one point, it says it can't see or read or something the file. That's because it literally "can't see" the file. It's like a maddening riddle.
So rip your battery out, and reboot, it will start up as normal. Your phone is not ruined. Then you can format the SD card. I bet that is what it is.
When you do get it formatted, you are going to be starting from scratch. You will have to login again with Google, which is how they get you to have to pay that big data plan. I had to do it again to get on. About to switch back, (11 dollar Dash plan works fine with WAP) then discovered Jesus Freke's Rev 1.42 someplace. Which supposedly you can login using WIFI. So I have to find that again. If you know where it is.