1: press F11 to enter the system startup item and select the USB disk to start.
2:after reboting the U disk and entering the main interface of the U disk boot,use the keyboard up and down keys to select  to determine.
3: after entering the PE desktop, double-click the desktop 'Pure PE installation tool' icon to open the tool.
4: select the restore partition, select disk C as the system disk in the disk partition list, and then click OK.
5: click OK
6: then the program will start to release the system image files. We just need to wait patiently for the operation to complete and restart.
7: after the release is complete, the computer will restart, and will later continue to perform the subsequent installation steps of installing the win7 system. After all the installation is completed, you can enter the win7 desktop.