Installing DirectX 9.0a appears to have caused periodic hang.

Hi Experts
    System Me 4.90.3000           800Mhz AMD Athlon          Carrera Octan.
Previously had replaced a faulty HDD (with apparant slow spin), formatted & reinstalled Me to fix a number of problems including System Restore and MS Updates.     Am using ZoneAlarm.    Installed all appropriate MS Updates & various applications including troubleshooting 'Tools'.
Now have a 48 sec boot, instead of > 15 minutes  :-)  
System Resources 84% Free, falling to ~60%(typical) after ~ 5 hours of use.  Functioning well .... that is until I installed DirectX 9.0a (FlashGet).  Immediately ran into hang and permanent timer, displayed for approximately 50% of all attempted boots.   No errors were indicated.    Used 'Reset' to S/Down & thus enabled ScanDisk.
     Surprisingly the problem has actually reduced over a period of several days!  Have not yet used any of the available, daily system Restore Points, as I'm not sure of the effects on DirectX 9.0a, quoted as 'you can't uninstall'.
     Any ideas please; is there a known fix for this condition?  Surely it's not possible for there to be some software mechanism that partly resets or restores the above fault condition?!!!   Reason I ask, I noticed a similar situation 17 months ago after installing DirectX 8.0 on this same computer.    Then, bootup & Display Resolution were affected (permanently set at 1024x768).  Here too the bootup condition significantly improved over the following weeks!  
   Reinstalling Me is not really an option.        Thank you in advance.            Jonvee