CD-Rw not always reconized

I have a Compaq Presario Desktop SR2163WN with Vista Premium,about 1 year
old. My problem is installed a second CD-RW Drive and was working fine. Than
one day after rebooting it was missing from My Computer.I restarted PC than
is was back there. I updated the driver and rebooted and worked fine for
awhile than stated all over again,missing from My Computer. I opened PC ,made
sure everything still plugged in ,ok,everything fine. I don't know what to
try next. Sometimes when I shut down and turn back on it will be back again.
Any help would be great! Thanks