Use MSConfig, go to the General tab, click the Advanced button and check the box "Enable Startup Menu". When you next boot your system you will then automatically be present with a menu where you can choose whether to start in normal or safe mode as required.
Having lost myself in the Microsoft support items which are a bit beyond my ferreting out the applicable items, I did read if this fails reinstall windows98. There seemed no end of reasons from hardware failures etc. etc.hence my remarks. Thanks for your time Charles, I reckon I will live without Safe Mode meantime. If the ultimate failure occurs then I can start from scratch! Regards, John