Router login page open up automatically when I connected to the network

I'm using Router Tenda W309R http://www.tendacn.com/in/product/W309R.html

Every time I restarted the router, as soon as I connected back to the network a web browser on my computer opened up automatically to 192.168.80.1/index.asp

This is a router login page that came up when I connected to the network:

I have Mcafee Antivirus + Firewall installed on my PC. I have run full scan and no malware came up. I ran MalwareBytes Anti-Malware found only OpenCandy Ad-Ware which has nothing to do with the router

Malwarebytes Anti-Malware www.malwarebytes.org

Scan Date: 7/02/2016 Scan Time: 6:42 PM Logfile: Administrator: Yes

Version: 2.2.0.1024 Malware Database: v2016.02.07.01 Rootkit Database: v2016.01.20.01 License: Free Malware Protection: Disabled Malicious Website Protection: Disabled Self-protection: Disabled

OS: Windows 8.1 CPU: x64 File System: NTFS User: E5

Scan Type: Threat Scan Result: Completed Objects Scanned: 395511 Time Elapsed: 5 min, 3 sec

Memory: Enabled Startup: Enabled Filesystem: Enabled Archives: Enabled Rootkits: Disabled Heuristics: Enabled PUP: Enabled PUM: Enabled

Processes: 0 (No malicious items detected)

Modules: 0 (No malicious items detected)

Registry Keys: 0 (No malicious items detected)

Registry Values: 0 (No malicious items detected)

Registry Data: 0 (No malicious items detected)

Folders: 0 (No malicious items detected)

Files: 2 PUP.Optional.OpenCandy, C:\Users\E5\AppData\Local\Temp\is-QKG4I.tmp\OCSetupHlp.dll, , [697470ed0693ef47cc404aa5f1135aa6], PUP.Optional.OpenCandy, C:\Users\Public\Downloads\AxCrypt-1.7.3156.0-Setup.exe, , [49947edf188137fffb11a7487b8917e9],

Physical Sectors: 0 (No malicious items detected)

(end)

How does this work? How can a router issued command to my computer to open a web browser and open a web page? Could anyone explain this to me?