Do not invest any money into this PC.
It is soooo old even if you overclock the CPU to 4 GHZ it still wouldn't make a difference.
The reason for that is because the CPU is based on an old and painfully slow archetecture and also because since you didn't mention your graphics card, i assume you're using one that's intergrated.
And even if you're not the Pentium still won't cut it.
Either scrap this build or use it for work. It will not play new games no matter how much you overclock it.