The 12 volt section of a PC supply most likely will not have enough amps to run a CB set.
The guys here suggested some ideas. Here are some useful tips.
Keep in mind, years ago I was a cb repair expert. So I have a clue.
Avoid switching power supplys.
Many radiate stray energy and will interfere with operations.
Get a classic linear power supply. These guys are ok.
There is an indoor antenna on Amazon that has gotten some good reviews.
Just a little detail, on this kind of antenna, when they recommend a minimum coax length, follow it.
One more thing. Stuff effects radios, and conversely radios effect stuff.
Your signal is going to get into things.
Expect computer based devices to mess up.
PC's won't like it very much.
Stuff in a plastic case will be less well shielded than metal cases. Speakers may make noise when you transmit.
Expect people to bitch, your neighbors in particular.
Im going to add a CB to the work bench but not for transmitting. RX only.
So a six foot bit of wire tossed into the corner will do the trick.