You might try unplugging the other USB devices.
If you have several devices that are drawing power from the USB, it can cause a problem.
If you are using a USB hub, it should be a powered hub.
Here is a link to a site that has a USB troubleshooter:
http://www.usbman.com/
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System: Dell Dem 4100, PIII, 866mhz, Win ME, USB 1.1
I just got a Pentax *ist DS. I installed the pentax browser and lab software. I followed the instr. for the camera transfer settings but no luck. With the camera hooked up and turned on I do not see any additional drives in my computer. I went to the control panel and used ADD HARDWARE, it recognized it as an *ist DS camera but said that there was an error - "driver needs updating". I tried the update button but it did not find anything. I went to Dell for driver updates but I do not recoginize what to get- would it be a USB driver or what? Pentax says drivers are only needed for Win 98.
My USB seems to be OK since my HP scanner uses it without a problem. I had a game pad /controller plugged in to that USB port previously and it seemed to work.
I have emailed Pentax cust. support but have not had a reply yet.
Any Ideas ?

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