Hi
My SSG5 reboots all the time.
Every time after loading it reboots.
Start loading...
.................................................................
.................................................................
..................................................
Done.
Juniper Networks, Inc
SSG5/SSG20 System Software
Copyright, 1997-2008
Juniper Networks SSG5 Boot Loader Version 1.3.2 (Checksum: A1EAB858)
Copyright (c) 1997-2006 Juniper Networks, Inc.
Total physical memory: 256MB
Test - Pass
Initialization - Done
Hit any key to run loader
Hit any key to run loader
Hit any key to run loader
Hit any key to run loader
Loading default system image from on-board flash disk...
02%
Before that I couldn't get to router via http, ssh. It didn't answer ping request. But I could login through console.
I did reset to factory default and downgrade firmware to 6.2.0r19.0 from 6.3.0r21.0 and it started behaving like that.
I had left it without power for a night and today it started normally.
In console was:
Load Manufacture Information ... Done
Initialize FBTL 0........ Done
Load NVRAM Information ... (6.3.0)Done
Install module init vectors
The device is storing the firmware into reserved flash sectors.
Please do not power off the device during this operation. Doing so could result in loss of firmware.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+++++++
The device successfully completed the operation.
Install modules (01148800,020a0198) ...
PPP IP-POOL initiated, 256 pools
Initializing DI 1.1.0-ns
w3g_cfg_init
System config (1390 bytes) loaded
Done.
Load System Configuration ...................................................................modem is not detected
..................................Disabled licensekey auto update
....
Unsupported command - set snmpv3 local-engine id "0162072008003836"
.........Done
system init done..
login: System change state to Active(1)
But after turn off from power it doesn't start normally again.
Do you think it's time to change device to new one? 
Marcin Gruszka