not tried this myself but I have found this on another forum.
If nothing works, not even "force", then:
Connect the receiver to your PC with Null-Modem (Cross-Wired RS232) cable
Open a Terminal application (Like PuTTY)
Select your COM port, set the baud rate to 115200 and open the connection
Turn the receiver ON
When you see the 'PK7105' prompt, copy the following command without the quotes ("") and press ENTER:
"set bootargs console=ttyAS0,115200 rw ramdisk_size=6144 init=/linuxrc root=/dev/ram0 nwhwconf=device:eth0,hwaddr:00:06:37:04:15:00
ip=192.168.40.83:192.168.40.19:192.168.40.1:255.255.0.0:lh:e th0
ff
stmmaceth=msglvl:0,phyaddr:1,watchdog:5000 bigphysarea=6000"
When you see the 'PK7105' prompt again, copy the following command without the quotes ("") and press ENTER:
"nboot.i 0x80000000 0 0x00100000 ;bootm 0x80000000"
The receiver should boot to SPARK
Upgrade the receiver to the "spark_1.2.54 Europe" version (This is
important!)