1. There is an invalid signature in the security startup policy. When starting the machine, press F8 to enter the safe mode, and then recover to a problem-free time period through the system recovery in the safe mode.

2. The computer shows invalidsignaturedetected. Checksecurebootpolicyinsetup: indicates that the computer shows that an invalid signature has been detected. Check the security boot policy in the installer. There may be something wrong with the computer system, so this system needs to be reinstalled.

3. InvalidSignatureturetedChecksSecureBootPolicyinsertup → Invalid signature detected. Check the security boot policy settings. This is the prompt that the driver is unsigned.

4. This is the BIOS setting of the motherboard. You can press F 10 to save and exit.

5. If win8 machine is pre-installed and win7 system is modified, it is suggested that you change the BIOS security option settings: press F2 to enter the BIOS, set Boot-LunchCSM-Enable, security-securebootControl- Disable, and then press F 10 to save and exit.

6. Use a USB flash drive to do pE on other computers, but Baidu Master U can download and install it. The USB flash drive is plugged into this computer, and the boot setting is that the USB flash drive enters the second pE. Close the pop-up interface, open the system repair, and repair the C disk. Restart the computer and unplug the USB flash drive.