c140 "USB Device Not recognized" msg

Have a Dell P4 1.6GHz maxed at 512MB DRAM w/ USB 1.0 resident.  When I connect my c140 (with power OFF, per Sandisk’s instructions) I get the Sandisk “power logo” and the c140 goes straight to my first mp3 file instead of displaying the “MTP Connection Mode” screen.  I then get a “USB Device Not Recognized” message on my PC monitor and cannot access the c140.  This happens intermittently.  Sometimes rebooting the PC helps, but not always.  I have tried the battery removal and reset routine, but get the same result.  Sometimes I can go days without this problem, then it resurfaces for no apparent reason.  Any (realistic) suggestions?