LS-QVL failed to turn on and kept rebooting

[lexus_2004]

I have a LS-QVL with Raid5 of 4 2T Seagate monitoring disks, FW 1.68. Yesterday I found the NAS cannot start properly after power-on but also keeps rebooting.
After pressing the power button, the blue LED keeps flashing, and the 4 disk LED indicators turns green in the first place. Then in the process of starting up (blue LED keeps blinking), the 4 disk LEDs turned off and then start to turn to green again one by one, but the forth disk (disk 4) LED did not turn to green. After quite a while, the NAS reboot and started over the above process again.

I tried to take out the 4th disk, the issue still remains. And also tried switch the 1st and 4th disk, still the disk 4 LED did not turn to green and NAS rebooted. Can anyone help on this issue?

Many thanks.

[lexus_2004]

Actually it keeps restarting again and again. Seems that it runs disk diagnosis every time and the system cannot be loaded in the boot process. NAS Navigator cannot locate the NAS on the net, nor does the LSUpdate. Although it seems that it detected the 4th HD is loaded (all 4 Disk LED turned green at the first time after rebooting), it some how cannot get the 4th disk online. (The Disk 4 LED did not turn green in the one by one disk getting online procedure? even after I switch the 1st and 4th HD).

Has anyone ever got this issue? Is it the problem with the hard disk or the LS-QVL? Would the data on the Raid5 array be still complete? How can I get the system online?

Thank you very much!