I have a client who is experiencing the strangest "hang" problem I've ever run across. When it hangs, the mouse pointer still moves, the Start menu still responds, system tray icons will pop up their menus, and ctrl-alt-delete brings up the Windows Security dialog. But when the Task Manager button is clicked, nothing happens except the security dialog goes away. Clicking on any menu item closes the menu, but nothing starts. The hard drive is not being accessed during this "hang" period, and since I can't get Task Manager to start I can't tell if the CPU is doing anything. The only way to powerdown the machine is to hold the front panel power switch down for several seconds until the machine does an abrupt power off. Then, the next time the machine starts, it takes several minutes (four or five times longer than normal) for the machine to reboot into Windows. The machine does not indicate it is running chkdsk/scandisk, but I can't tell what it is running that takes so long.

Operating system is WinXP sp1. Various applications used through the day are AOL 9, MS Office 97 sp2a, Roxio, QuickBooks. Computer is an E-Machines Celeron (2.6GHz, 512meg RAM) roughly 6-9 months old. Both AdAware 1.06 and Spybot 1.3 think the machine is whistle clean, as does AVG 7.

The time since boot it takes for the problem to occur varies from thirty minutes to several days. Cold booting the machine is the surest way to correct the behaviour. The computer developed this problem over multiple weeks, with no hardware updates in that time, and few if any software updates.

I'm stumped as to how to proceed.