Repair is not the psychic friends network.

A model that old is not worth the time to repair @  $75 dollars an hour or more.

You should start by learning how to make puppy linux cdrom bootable media.

Lupu 5.2.8.005 -> http://diddywahdiddy.net/Puppy500/lupuplus-528.005-1.iso

This cdrom doesnt require a lot of ram and will boot and run without any hard drive installed.

While there might be someone willing to be looking at posted pictures and doing psychic computer repair I am not.  Basic repair is the same for almost all models from 2003 to now.  DL2032 battery is the first thing that should be replaced.

https://www.dell.com/support/article/en-us/sln130418

https://www.amazon.com/Fresh-Duracell-DL2032-Lithium-Batteries/dp/B016KQYM8I/

I can get these everywhere all day long without needing to order it from amazon but your situation may be different from mine.  Grocery stores have these because blood sugar measurement machines need them.

https://www.dell.com/support/home/en-us/product-support/product/optiplex-745/docs

https://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-745_user%27s%20guide_en-us.pdf

1. Ultra Small Form Factor (USFF) Front View
2. Ultra Small Form Factor (USFF) Rear View
3. Small Form Factor (SFF) Front View
4. Small Form Factor (SFF) Rear View
5. Desktop Chassis (DT) Front View
6. Desktop Chassis (DT) Rear View
7. Mini-Tower Chassis (MT) Front View
8. Mini-Tower Chassis (MT) Rear View
9. Back panel connectors

https://www.dell.com/support/article/en-us/sln285003/dell-optiplex-745-system-guide?lang=en

https://www.dell.com/support/article/en-us/sln285046/dell-optiplex-745-visual-guide?lang=en

https://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-745_reference%20guide_en-us.pdf

While I appreciate it, @speedstep, but this is a repair for myself. And I'd be able to attach pictures of needed. I have the guys of this computer all around me at the time of this writing this. And all I need is information

I have dissembled and reassembled about ten 745 DT and SFF models.  what you did is correct by cleaning dust. next thing is to pull out all ram sticks and only put one back in DIMM slot 1.  Reset CMOs jumper on motherboard if you find it. Then try to turn on power to see it would POST. If yes power off drain power from system by pressing power button, add more memory sticks there are.  It is old pc but if it has c2d, can still run Win 10 64bit.  For more in-depth repair I might apply new thermal paste after first cleaning old paste away using 99% isopropyl.  Do not use 70%. Unfortunately now hard to find 99%. If cpu fan is not loud, I might postpone thermal paste step till future.

@JamesBronie  it sure would help the community assist you better if we knew what you needed help DOING.  Is the computer not powering up?  Is it giving you a blue screen of death?  Is the hard drive slow and noisy?

Kudos for pulling it apart and dusting it.  Now you need to get more thermal paste on that CPU, reassemble it, and tell us what your issue is with your machine.

We can't help if we don't know what's broken.