Question: how to start computer in safe mode windows 7 f8 not working?
Answer: Boot into your Windows (Vista, 7 and 8 only)
Go to Run. ... 
Type msconfig.
Press Enter or click OK.
Go to Boot tab.
Make sure the Safe Boot and Minimal checkboxes are checked, while the others are unchecked, at the Boot options section:
Click OK.
At the System Configuration screen, click Restart.