Ouch - that's a real bummer. I've got an iPaq 4150 and I notice it sometimes won't come on either - a soft reset usually sorts this out. I can't decide if its the hardware or PocketPC2k3 is a POS.
In case you haven't already, how about trying a soft-reset?
I ActiveSync wirelessly on my iPaq 4150. Writing files to main memory is faster than the SD card, but neither appears to be fast enough to saturate 11Mbps.