OK.. You've Asked a BIGGIE......
Machine should have been "wiped clean BEFORE being sold for the safety of the previous owners info. Because it wasn't, I'm going to assume it could be also be loaded w/ viruses/trojans etc.Common cause of trashing/selling a computer.
The problem w/ wiping clean is : CLEAN!! No Operating System at all!
If you do this you will need to buy a new retail version of a suitable
OS ($$$)for machine. Depending on model, age & specs (which you don't give) MAY
be able to take XP (min.512RAM? HD of 80 Gigs?) or not. Most UNlikely it is Vista compatible.
I assume you don't have original install disk w/ key (I you can get it, that would be very good). KEY may be on sticker on bottom or back of machine. Possible that it didn't have OS disk to begin with. Instead, back-up of original OS may be installed ON MACHINE in a separate partition (example Drive D or ?). If so, you can "Burn" a copy of it
(export) that to several CD-R's(4 or 6?)or fewer DVD R's(1 or 2?)if it has a burner.
This would be ideal!
Additionally, depending on age & OS, you maybe able to do a reformat to original factory conditions by using a process internal to original install. Often under " Start>All Programs>Accessories>System Tools" or in on-machine "help files" or go on line and look into "support" at manufacturer's site for info re this (or possibly it's in owners manual viewable/down loadable online ).
This would dump all except what the factory installed originally.
Great patience would be a great character trait to exhibit at this time..but it is doable. You really need to get all system specs you
can to safe guard.
As a first computer, I must applaud your courage at attempting this.
Would be VERY helpful IF you know a "Nerd" friend who has done similar to help you with this.
You may post back with more questions BUT we need ALL current system Info possible to be able to give more specific suggestions. Sandy