There are some instances of this problem online, with this model computer.As I understand it, the system resets instantly, ie stops, posts and restarts whenever a USB drive gets attached. Mouse, camera, etc all work ok. The thumb drive works.I cant seem to find any coherent answers to the subject, but I can offer a couple of guesses of my own.a: corrupted drivers, in which case you need to reinstall the drivers.b: its a problem caused by a USB2.0 port running at reduced speeds, also likely a driver issue.c: its a problem because the port could be actually physically a USB1.1 port, not a USB2.0 port. Are you plugging everything back into the same USB ports you used to plug them into?Is it possible that you used to plug the external drive into a rear port and are now trying to plug it into a front port, or vice versa? If thats the case, please try putting them back into the same ports they were previously and see if it helps.d: there is a power supply problem via the USB port. Does the external drive have its own power supply, or does it draw its power via the USB? What happens if you plug a powered USB2.0 hub into the USB port, then try to run the drive through that?Here is what I would do. The HP website certainly says that all models of the D510 have USB2.0 front and back, so hopefully we can disregard option C. First, reinstall the USB drivers using your motherboard disc. Restart and then try the external drive again, using a rear port. Rear ports are a part of the motherboard, whereas front ports are connected to the motherboard via cable. The rear port will be more reliable.If this is hasn't helped, then I would try borrowing a powered hub. This is a multiple USB socket, with 4 or 6 USB ports usually, which has a power supply of its own and a lead to connect it to a USB port. Connect it to a rear USB port, turn the power on for the hub, and try connecting your external drive via the hub. If this works ok, then we know that the factory USB system is not supplying sufficient power via the USB connection. If this is the case, it could be for a number of reasons. One is of course the physical health of the USB port and of the plug which comes from the external drive.Another could be that the power supply of the computer is failing. Computer power supplies emit varied voltages via different connectors, which supply different components with the power levels they require. Its possible for some of the power supply outputs to work well, while others dont. Longer term though, if one part has started failing, the rest is likely to follow soon. If this seems a possibility, any competent electronics repair guy should be able to test the power supply for you.I am sorry I can't be more helpful at this point, but as we gather information and try things, I'm sure we will work it out.
Mitz from Tips4pc