Hi, I am a 15-year old robot enthusiast from India. I am currently building a demi humanoid robot and I was in search of a microcontroller. I tried using Raspberry Pi but it was not enough for me. My next option was to use Nvidia Jetson Nano, but it was really expensive. It was around 335(approx.) in Amazon. For Indians like us, 300 dollars is highly expensive. Since I am a student and not having a job I am living under my parents and have no source of income. My parents cannot afford to buy this Jetson Nano. Recently, I found my old PC lying around. I was thinking if I could use that as the controller for my robot. If yes, could you please explain how can I do it?
Hello @jairojosy and welcome to the RobotShop community!
It’s awesome that you are interested in robotics at such a young age 
May I ask why the Raspberry Pi was not enough for you?
I don’t have experience repurposing an old CPU for controlling a robot so I won’t be able to give any advice in that regard, however as you are building a humanoid I thought this topic could be of interest to you:
https://community.robotshop.com/forum/t/lynxmotion-ses-v2-humanoid-robot/
And here are some boards that might interest you:
As you already have a Raspberry Pi you could try adding a USB Stick/Dongle to add some extra processing power (you can find some options in the link above)
I hope that helps!