sluggish performance on new dell optiplex 780s

I have a set of 4 dell optiplex 780's running windows xp sp3.  The users are reporting that there is often sluggish performance, and that there are occassional, random, undesired reboots.  I have verified that the reboots are not due to automatic windows updates (which are set for 3am).  When it reboots, the user says that it says shutting  down, and does not just go black.

The resources on these PCs are good, with 4gb of ram and quad core processors.  The only reason we got xp and not windows 7 was due to certain software that still needed XP.

I did notice some preloaded software that came on these desktops:  Dell control point software, dell security device driver pack, intel active management technology, intel network connections, and intel matrix storage manager.  Not sure if removing any of these might help.  (I was leaning towards trying to remove the dell control point software)

I have run some malware bytes scans, that came up completely clean.  No malware detected.

In any event, these are heavy users, and have important roles for their PCs, so I really need to get these issues resolved.  If anyone has any ideas, please help!  ( I will be working on these PCs monday morning, if anyone could help )