The problem cannot be solved by installing Altera USB blster.

The original version was installed on the quaruts8.0 web system, but the compilation was too slow, so I wanted to switch back to 7.1. After the installation was completed, I did not find the USB blster during programming. The re-plugging was ineffective and the hardware device was turned on, an "unknown device" is found in the USB system, and the system prompts that the device name already exists. Uninstall. the reinstallation is invalid. Some methods on the Internet were ineffective, so I decided to manually delete information about USB blster from the system. Step 1: Delete the driver file. Windows/system32/Drivers/ftdibus. syswindows/system32/ftbussui. dllwindows/system32/ftd2xx. dll Step 2: Clear the information about USB blster in the registry. Find all items in the Registry about "ublst" and delete them. Specific Method: use the search ublst to find one and delete the entire item in the directory tree. Because USB is an out-of-the-box device, even if you delete multiple files, a prompt will be displayed after you insert them again. However, You 'd better back up the Registry first. Step 3: restart and reinstall the USB blster driver. OK!