Here we go again... (there was a thread here recently about reading from the serial port).
You're telling it to only read one byte:
ReadFile (m_hCom, Byte, 1, &dwBytesTransferred, 0);
and dwBytesTransferred is filled for each read - it's not cumulative, so you're making an infinite loop...
(dwBytesTransferred will always be one because you're only asking for one).
Addendum:
http://forums.pocketmatrix.com/viewtopic.php?t=10086
