Honestly, I think the issue probably is Vista. I don't like to blame Vista normally, but I think this may be the case.
The Pentium chip is definitely not the fastest processor out there, far from it. I know my old Vista machine with a Core2Duo was very slow until I did a clean install on it. Even then, it's not the fastest thing.
Do you have the original disks that came with the computer? If so, what disks do you have? If you are comfortable, I would possibly recommend a full clean install, rather than just a factory restore. This will give you the cleanest possible install.
If you're interested, a tutorial on how to do this can be found here:
https://www.sysnative.com/forums/wi...-install-windows-windows-7-windows-vista.html The tutorial does show Windows 7 screenshots, but the process is exactly the same
I have done quite a few Vista clean installs, it's not quite as scary as it may seem.
This is purely up to you, it's just an idea. It may or may not help, but it will give you the lightest and cleanest install possible.
If you do decide to, and you need assistance, I'll be more than happy to guide you through it.
Regards,
Stephen