4 red beeps upon startup followed by silence, and repeat.

[Ineedtofixmypc]

A pretty old PC that tends to overheat and run slow. An HP Compaq 8300 small. Giving it a slam in hopes it works faster, which used to work before, genius engineer skills, I know, it shut down. Tried booting it up and it gave me 4 red beeps. I cleaned it up inside, unplugged and plugged RAM, power supply and the outer back cords. Is the problem: the power supply, the CPU, or anything under/related to the CD box? Or anything else, really.

[SDH]

HP BIOS tends to use a specific number of beeps and red led flashes to help diagnose issues. A great starting point is via:

https://support.hp.com/us-en/product/details/hp-compaq-elite-8300-small-form-factor-pc/5232852

The technical and service manual for that series of workstations includes the 8300 Elite Small Form Factor:

https://h10032.www1.hp.com/ctg/Manual/c03612798.pdf

That is the version 2 of the manual and on page 259 you'll see:

Search for "beeps four times"

HP tells what to do, above, to fix it. That can be due to an internal power supply issue and replacement recycled power supplies are easy to find on eBay for under 20.00 USD including shipping. Try the other easy stuff first.

It is pretty easy to improve performance with those Elite 8300 SFF computers by making sure you're running a SSD instead of a HDD (such as 512GB Intel 545s or Samsung 500GB equivalent) and replacing whatever slow processor you have with the fastest HP certified for it, the Intel Core i7-3770 (page 6 in the attached QuickSpecs v20). Max speed is 1600 MHz for that processor, 32GB max amount of RAM, and there is only one sSpec code to look for (SR0PK). You also want proper type HP matching-speed memory... can help you with that if you wish. These are a sought after processor but you can find them from good US sellers on eBay for under 30.00. An excellent small form factor video card to use in those is the nVidia K620 which is what is in ours in the kitchen area for quick access:

Excellent processor...Excellent small nVidia video card...

That card (under 20.00 USD on eBay) still is getting driver updates from nVidia, has a little nVidia Display Port firmware update v1.1 that works nicely, and has worked very well in our 8300 SFF for years now. We're running W11 Pro, installed using Paul Tikkanen's method described in the forum here (uses Rufus). There also is an easy way to update the 8300 BIOS to the latest, from within BIOS, if needed and I'd do that before upgrading the processor.