An antivirus program will scan your disks and files and tell you if there actually is a virus and can remove or correct the problems that it has caused but the best defense against a computer virus is a little preventative action on your part. First, if you do not already have an antivirus program, invest in one. Antivirus software is not perfect but no computer in today's world should be without it. Or go to the web site of one the popular commercial antivirus programs. Once you have an antivirus program installed, be sure to update it frequently as new viruses appear all the time.
Most programs offer updates online through their web sites.
Second, be wary about putting floppy disks from unknown sources into your disk drive. Scan every file on the disk, not just the application files. Running an antivirus program will not harm any file or program on the diskette. CD-ROMs are less risky, but you can also scan them before the first time you use them. Third, download with care.