Friend, this is because your computer deleted the system file by mistake, or the system file was destroyed by a stubborn Trojan horse! (Original answer, original author: Dance Demon Ji Fen Dance Demon) Tip: If the first aid kit can't connect to the Internet, use "offline mode"! 1. Download a "360 system first aid kit", and friends who have installed "360 security guards" can directly open the "360 system first aid kit" under "Trojan horse killing" and "custom scanning", and click: 1. Start first aid! After the first aid, deal with it immediately and restart it! 2。 "File recovery area" after boot, completely delete files! 3。 "System Repair", select all, and repair immediately! Key 4. Network repair, start repair, restart the computer! Key 5. Dll file recovery, scan, if lost, add recovery, if not! 2。 Use "System Repair" of "360 Security Guard", click "IE Common Settings", "Modify Home Page", "Navigate with 360 Security Website" and click "One-click Repair"! 3。 Use "Scan Plug-ins" of "360 Security Guard", and then click "Clean Plug-ins" to delete "Bad Plug-ins"! 4。 Use "360 Antivirus Dual Engine Edition" again, check "Automatically handle scanned virus threats", "Full Scan" and "Custom Scan", and click Delete! After restarting the computer, enter the "quarantine area" and click "Delete completely"! 5。 Trojan killing horses, "full scan" and "custom scan" If a Trojan horse is killed, deal with it immediately! Restart! "File recovery area", completely deleted! 6。 Nothing more, try: Jinshan first aid kit, check "extended scan", deal with it immediately, and restart the computer! 7。 Nothing more, try: Jinshan net shield, one-click repair! 8。 Really not, only: one-click restore (method: visit my "Baidu Space" blog) or reinstall the system!