Hello Hilary,
There is a possibility that the this issue is caused by a virus, malware, and etc. Certain malware can interfere with your internet connection or change your proxy settings without your knowledge. Since you've already run some malware tests and wasn't able to detect any infections, kindly try to perform the steps below:
You can reset Internet Explorer settings to what they were when Internet Explorer was first installed on your PC. This can be useful for troubleshooting problems that may be caused by settings changed after installation. Note that resetting Internet Explorer isn't reversible, and all previous settings are lost after reset.
- Close all Internet Explorer windows. Select the Tools button, and then select Internet options.
- Select the Advanced tab, and then select Reset.
- In the Reset Internet Explorer Settings dialog box, select Reset.
- When Internet Explorer finishes applying default settings, select Close, and then select OK. Restart your PC to apply changes.
If the issue persists, try to disable the proxy setting and check if you can browse the internet:
- Press Windows key + I, then select Network & Internet.
- Go to Proxy, turn off all the options.
In addition, it would also be best to run a scan using Windows Defender to make sure that your system is free from any threats.
Looking forward to your response.
Regards.