Server 2003 Standard ntbackup intermittent failure to external HDD

I have a Windows 2003 Standard Edition 32-bit Server with SP2 installed using ntbackup to external harddrives.  This worked great for the first 3 years no problems ever.  Then the power supply failed for the drives and would not detect any drive.  The power indicator on the drive would turn on solid but nothing else.  Connected to any computer it would not work.  Connected one of the 2 remaining power supplies from set of 3, and everything worked again for awhile.  Then the problem became that ntbackup would only backup partially and the logs would be completely blank for that night.  The nights that did backup successfully could not be correlated to any drives.  (i.e. Drive would work one night and not another, drive 2 and 3 would do the same).  I have sinced replaced them with brand new drives and power adapters which worked for about a week and then the same thing started and has been happening for several weeks now.  I have the /um switch in the scheduled backup using task scheduler.  On 2 occasions at night I have forced a backup successfully and then let the scheduled backup run (successfully).  With the new drives I might have slightly better success 3 to 4 days per week will work vs. the old drives only obtained 2 to 3 days would work (5 day schedule).  I cannot find any open files before the scheduled backups run and cannot watch them every night.  I did find information about a hotfix from microsoft, but I am not sure it actually applies to me.  The size of the failed backups varies.  I have other 2003 servers with identical setup and they are still running after 2 to 5 years without problem.  Server is DC with less than 15 client PCs.
I am including system state in the backups (approx. 9GB when successfully backedup / 13GB data)