I can take your description of the trouble you are having with your computer and translate it into a plan on how to solve the problem. Many times, computers can be optimized with just software, de-duplication of files and a few tweaks. Those are the easy problems to fix. Unfortunately, sometimes, the computer problems are hardware. It may be a power supply, (yeah, I've replaced those), wifi card or it could be a driver problem that renders your hardware somehow inoperative. I've dealt with all those situations and more. Most of the computers I own, I have either built or refurbished. Not only the hardware, but also the software and/or the operating system.

I can not fit 2 gallons of water in a 1 gallon pitcher. If the computer's drive is full, it will not work correctly, but I am able to diagnose that and give you guidance on how to either:
a) better manage the space you have or
b) upgrade the storage to your computer

I replaced the hard drive on my PlayStation3, and it's been money well spent. Long story short, I've had to make my old computer equipment last a very long time (the computer I'm using currently is from 2009), and am a firm believer that I don't need to buy computer equipment frequently in order for it to work well.