Processor problems, working at 100%

Hello everyone, I recently decided to revive my computer by buying a GPU
the specifications are as follows:

Motherboard: Asus m4n78 SE
Processor: AMD Athlon II X2 250 3.00 ghz processor
Ram: 2x2gb ddr2
GPU: XFX GT-630N-ZDF2 GeForce GT 630 1GB GDDR3
Windows 7 ultimate 64 bit

I bought it like 2 weeks ago (it is a second-hand gpu), the first week everything worked fine, I played light games like the league of legends, I did word and autocad work until overnight when doing these activities the pc hung at times, jerks of 5 seconds and then returned to normal, for example in a 40 minute game I had jerks 7 times where the fps were still stable (60) but I could not move the mouse pointer or give orders With the keyboard, download the afterburner and playing lol I obtained the results of the images, the gpu between 30 and 50% while the cpu at 100% it should be noted that the same thing also happens browsing the internet or when I open applications such as autocad but less frequently, I already tried formatting the pc and deleting all the files from the hard disk but I still have the same problem, what can I do? change the processor? the gpu? From already thank you very much!