Depends on how the person or company built the computer that you
bought from them.  Depends on make and model.  Read the manual on how
to recover or restore your system, or call whomever built your
computer.  And if you also, ahem, "lost" the manual then go the
manufacturer's web site to see if they provide an online copy of the
manual.

It depends on the supplier. Some sell their PCs with a
recovery facility, others don't. You need to read the
manual that came with it when you bought it.

Any solution is likely to require the cd.  When you find it be sure this
time to make a copy.