Comprehensive and Detailed In-Depth
The two best first steps are:
Perform a virus scan - Multiple users on a device increase the risk of malware, which can cause performance issues.
Check the startup programs - Unnecessary programs running at startup can slow down the system.
C . Back up the data - Important but not the first step for performance troubleshooting.
D . Disable the guest account - May prevent future unauthorized use but does not immediately fix the current issue.
E . Update the firmware - Firmware updates improve hardware stability but are unlikely to fix a sudden performance drop.
F . Reinstall the operating system - A last resort, as it erases data and takes significant time.
Reference:
CompTIA A+ 220-1102, Objective 2.4 - Malware and Security Threat Removal