WIN98

I HAVE A PC USING WINDOWS 98 OS.I HAVE BEING USING THIS FOR THE PAST MONTHS NOW.RESENTLY IT DEVELOPED A PFOBLEM IT BOOTS TO DESKTOP AND DISPLAYS A MSG AS EXPLORER HAS PERFORMED AN ILLIGAL ACTION AND WOULD BE CLOSED BY WINDOWS AND THAT’S IT NO ICONS WOULD BE DISPLAYED.I TRIED TO REPAIR THE INSTALLTION AND IT WORKED FOR SOME FEW DAYS THERE IT APPEARS AGAIN WHAT SHOULD I DO TO REPAIR COMPLETELY.