Informix just STOPS?

Running OnLine 7.23.UC1 HP UX 11.0 D250 X 2, Gig RAM When running, well, just about anything that takes a while and results in lots of reads (buffer, page, whatever) the damn engine just stops and sits there. For example, I just ran an update statistics for table(tabname) from the ISQL menu. Table is fairly large (120 million rows, about 8 gigs of space). Process runs for a few hours, then just stops. ISQL window sits there with Running... displayed. If I look at onstat -u I see the process, flagged as in a Read mode. nreads and nwrites never increment. Using HP Glance I see the system working hard when the process starts, avg 40% CPU utilization, 75% disk utilization. Then, boom. CPU activity drops to idle. No indication that anything has hung, resource run out, I have no clue. Various onstat -g options indicate the process is running, but nothing happens. This is a development box, there is no one else logged on, no other processes running but this one. Recently upgraded box from 10.2 to 11.0 in hopes this would fix the problem. Nada. Any clues or other diagnostics I can look at? Thanks, reply ray@apsnet.com