There is no way to do that without a disk.
However, your hardware may contain a backup. Please tell us the make and model of your computer, or list all your hardware.
Have you tried to run system restore, setting the drive back to a time before the computer became corrupted? Some of the new viruses prevent system restore from running, but it''s worth a try. Restore does not erase your personal files and is reversible.
click all programs
click system tools
click system restore
check the box that says restore my computer to an earlier time, click next
select a bold date on the calendar, a date before the problem started, click next
follow through with the restore directions
restart the computer after it finishes
if the system restore does not work, select an even earlier bold date on the calendar and repeat the procedure
try this with at least four earlier dates before giving up and trying something else