Yes, you will lose anything except for files on MemoryStick. As you can't turn on your phone, I'm afraid you can't backup your contacts (well maybe using FAR, but I don't think so). Also, try to restore GDFS using setool or FAR ;)

Edit: Be very careful when using SeTool, I bricked my phone (k750) using it (just restored GDFS using XS++, then it came back to life ).