My computer reboots randomly without warning and no overheating

If the Windows 11 or Windows 10 PC is restarting randomly, running a virus scan is a smart early step, as malware can deliberately trigger system instability. Certain types of infections, such as rootkits, bootkits, or ransomware, may cause unexpected shutdowns or reboots to evade detection, corrupt system files, or force updates to malicious code. Before investing time in hardware diagnostics, performing a thorough malware scan helps rule out software-based causes that can mimic hardware failure symptoms.

For the most effective results, use Windows Defender Offline or a bootable antivirus tool, since standard scans running within Windows may miss deeply embedded threats if the system crashes mid-scan. Windows Defender Offline runs before the operating system fully loads, allowing it to detect and remove persistent malware that could be triggering the reboots. 

If the virus scan comes back clean, you can confidently move on to checking hardware components like RAM, the power supply, or overheating issues. However, if threats are found and removed, monitor the system afterward to see if the random reboots cease. In either case, starting with a malware scan ensures you address the simplest and most easily fixable causes before delving into more complex hardware troubleshooting.

P.S. This is one of the most effective ways to fix computer reboots randomly without warning issue.