RAID 0 HDD misses sometimes

[HC08]

Hi, I'm using highpoint rocketraid 2340 create RAID0 using 10
Seagate ST3320620AS HDD in two mobile racks.
Using this machine for about 2 years, no problem occurred
though, recently the disks in one mobile rack can not be
recognized.

Though, pull out the disks in the mobile rack which didn't
recognized the disks, and turn the machine on. Then turn off,
and put the disks back to the mobile rack again, and all disks
can be recognized.

What can be the cause of this problem.