Reboot into safe mode with networking (press F8 during system startup) and run your web test. If everything runs fine there, you're almost certainly loading som

Reboot into safe mode with networking (press F8 during system startup) and run your web test. If everything runs fine there, you're almost certainly loading some piece of malware that's stealthy or malevolent enough to be hidden from the scans and inspection you're running during a normal boot. If you're still seeing broken performance in safe mode, then dig deeper with tools. But safe mode eliminates most driver issues and all but the most ridiculously sneaky malware.