Restored PC via "Recover" partition, but still lag, should I restore from discs?

Ok long story short, my wife's 4 year old Vista based consumer Dell PC was REALLY lagging sputtering, taking forever to do anything, whether local tasks like loading music and pictures and programs, to online browsing loading web pages, and temporarily freezing pages, etc. No viruses or anything of that nature.

I ended spending hours transferring all the files, pics and documents over to my laptop and restoring her PC to factory default from the recovery partition. That helped for about two days, then it was back to it's old tricks.

Will completely wiping the hard rive and restoring from the factory windows disks (which I still have) make any difference than restoring from the recovery partition? or perhaps is the hard drive somehow corrupted and time for a new PC?

Thanks