First, try un-plugging any USB devices(including keyboard, mouse, usb sticks, usb drives, hubs, printers, etc.) and see if it is one of them causing the problem.
Second, if the first does not solve the problem, try un-plugging the usb header cable(s) going to the motherboard.
If that does not do it, check the USB port on the rear of the motherboard and the surrounding area for anything foreign on the board that would cause a short or grounding problem(loose parts, wire pieces, screws, etc.).
Goto the USER CP for the TPU forum and fill out your specs and check the show button, too, as it might help some to troubleshoot.
Here is the website for your
ASUS M4A785TD-V EVO
Click on the download button there... and you can get a copy of your manual in a few different languages.
You, also, may want to flash your MB's bios to the latest, if you have not already done so.
Edit:
Also, you can try re-setting the BIOS(CMOS), by turning off the PSU and un-plugging it; then, remove the button battery, and press and hold down the start button on the case for about ten seconds.
Then, re-install the button battery, plug-in and turn on the PSU, press the start button and see if it fires up with no problem.
