ONLY showing using 1 core out of 4 core processor

I don't know a lot about computer hardware or software problems. I run a Dell Inspiron 20 All In One PC. Model 3045. It is a 4 core computer. In the bios and Device Mgr. only shows operating on one core. There is only one item entry. AMD A4-5000 APU with Radeon TM) HD Graphics.

A couple weeks ago PC acting weird - first, very slow. Odd messages: such as (not exact error message) Shutting down because of problem will restart. Adapter/Charger check. Bought new dell adapter and no difference

Had my local computer guy check and he is the who told me about only operating on one out of four cores per the bios and device mgr. Called Dell and they ran a diagnostic and advised hardware no problem. Wouldn't address issue of why then does it show only one core operating. Next I called MS and they ran diagnostic and confirmed software ok. They cleaned it up and ran somewhat faster, but not like a new machine.

Any direction you can offer would be appreciated. Dell is 2 1/2 years old.

Hi barbslife and welcome to Ten forums.

This CPUs aren't really fast, but should be OK for browsing and so..
I've searched a bit, and found one similar problem, but no solution to it.

Click on Start and type "msconfig" then click on program as it appears. Click on boot tab, then advanced and check if there are processors limited...

Open up task manager, select performance tab, select cpu.......then look at the bottom right of window. There you will find the info on your cpu......sockets, cores, logical processors and your cache. This is mine....a single processor with 4 cores that has hyper-threading which gives me 8 logical processors.

@barbslife
In Control Panel/Power Options, if you have settings at 'Balanced' or 'Power Saver', many cores will remain 'Parked' until needed, especially in Power Saver mode on Battery.
Experiment with the power options and monitor the cores in Resource Monitor/CPU Tab.
(In High Performance Mode, no cores 'park' themselves)

On the Task Manager view as in post #3
Right click on Graph and select > Change graph to > Logical processors.

One core won't be your problem. More likely are Malware, lack of application/software maintenance, poor basic specs.

Looks like you all missed in the first post from OP:

In the bios and Device Mgr. only shows operating on one core. There is only one item entry. AMD A4-5000 APU with Radeon TM) HD Graphics.

It means that only one core is recognized. Could be overheating and hardware failure or possibly option in BIOS.

I have a quad-core CPU with Windows 10 that only displayed 2 cores and 4 processors with Task Manager.
This remained the same no matter how many processors I entered in the BOOT Advanced Options of MSConfig.

I did some research on the internet about showing less cores than your CPU actually contains and discovered ParkControl.

I fixed the problem by installed ParkControl. ParkControl allows you to configure how many CPU cores are actually put in the parking mode by Windows. Now Task Manager displays 4 cores and 8 processors with MSConfig BOOT Advanced Options "number of processors" turned OFF.

ParkControl Free Tweak CPU Core Parking and Frequency Scaling in Real-Time