All-in-One Desktop, high disk usage?

We purchased DELL all in one desktop for our kids to use in 2018. This machine set in original box packed for 3 months before I opened it. After going through initial setup (all the updates etc.) I realized that it was very running painfully slow. I checked the task manger and witnessed CPU and DISK USAGE was 100% without even opening any app or software on the PC. I called DELL support and they tried to fix my issue for few days but nothing helped. After this, I demanded to speak Manager or higher up. Manger at DELL support assured me that they fill fix this issue but I have send this PC to their Computer repair center somewhere in Ontario. I did that. Techs ended up replacing the motherboard (on a brand new PC) and they sent this PC back to me. I went through the setup again and noticed slowness one more time. Upon checking the task manager, I realized the same problems CPU and HIgh Disk usage...

I got very frustrated with the situation and called the DELL support one more time. I demanded DELL to replace this garbage because it was unusable, unfix able.  After few calls, DELL replaced my PC to new one UNDER CONDITION that they won't be replacing my 2nd new PC if there are any issues. Only time you would use this condition when you know that your product has some issues and they are unfix able.

I have my new DELL PC now and I am having same problems. DISK USAGE is very high 100% most of the time and that is causing slowness. Also, I noticed on my 2nd PC, DELL has STOPPED some services so I don't see high CPU usage (How clever)

Overall, I am very unhappy, ticked off with All-in-One product. Dell wouldn't refund your money after warranty period is over. I don't understand that how a company like this size can create a such a bad product? Where is the quality control? Who is testing these products where they go out in real world? Does anyone has fix for high disk usage?