Try utilising Windows update (in Internet Explorer Tools), there may be critical updates you PC requires.
Microsoft no longer support W98 so don't know if you will be successful...W98 is flawed to the shithouse & as suggested by others you may want to upgrade to WXP. Even if you get your 'hang on shutdown' prob sorted I guarantee you you'll have other issues in the near future with 98. Bite the bullet & move on...you'll be glad you did!
