All NLM`s suspended

On a Netware 5.0 box with dual 450MHZ processors, 512 megs ram, Intel 440BX motherboard…RAID 5 on and Adaptec controller.We have run fine for a couple of years on this box and then about 1 month ago the server CPU utilization climbs to 38% and then suspends all the proceses and server.nlm ( all NLM`s ) get suspended. Have tried swapping RAM, new cables to hard drives on array. Nothing in any of the logs ( abend,syslog,volerr,tts , etc. ) so it`s really hard to pinpoint. Anybody out there seenthis or have any tricks to troubleshoot the problem. Thanks in advance