94 cadillac won't start, even with a jump. Battery is new and inside lights do come on, but vehicle won't start. Any advice? Thanks

When you replaced battery you activated the system. Need to read owner manual and see if it tells how to deactivate it. You may need to contact dealer to deactivate it.

Usually it means the computer is not accepting the chip in your key.
It can be the key, the sensor in the lock cylinder, or something in the security module or computer.
You might try another key or lock and unlock the driver's door with the key.

The PATS security system would prevent the engine from cranking if the system does not "see" the right chip in your key. If the system is working correctly, the light should go off after you turn the key switch on.
You should have power on the small starter wire when the key switch is in the start position.

When you jump started the vehicle, it started as normal and you drove to a shop to have a new battery installed.?? Correct??

1. Who removed the old battery and installed the new one?

2. Did the car start normally immediately after the new battery was fitted? How frequently were you able to drive the car on the new battery before the problem you described appeared?

3. Has anything been done to the vehicle since the new battery was fitted.?

You could have blown the main fuse while doing the jump start. Also check the fusible link on the power battery cable.

I suspect parasitic draw. All vehicles draw some power from the batteries when the car is shut off. Certain accessories such as clocks, radios remote door openers and alarms always need power. The normal power used is called parasitic draw.

It is always a very low draw so it doesn't run the battery down. If you install accessories like shortwave radios or plug things like inverters and portable refrigerators into the accessory socket and operate them too long without the engine running you can drain your batteries to the point where the engine won't start. If there is an electrical short in the vehicle or a malfunctioning accessory it could be drawing much more than its normal load causing a drain on the batteries. If you leave your door open and the inside lights stay on all night you could drain the battery down till the car won't start.

Here's also a good resource for your car specifically on narrowing down the cause of the drain.

probably needs a new battery

Did this occur straight after changing out the battery, or after sitting with the new battery installed?

Have you checked the new batteries voltage and voltage under load, eg. (Voltage when headlights are on) could be a flat new battery.

Or could be load on the battery after key is turned off, something draining the battery overnight like a boot or interior light, radio left on ect.

Unlikely a short, or you would be in a world of burnt wires from the battery cables.

Do you have any other lights, such as door lights or head and tail lights? If not the first thing I would check is the battery cable terminals. Over time corrosion will build up on the inside of the terminal lugs and not make contact. Even if they look clean from the top, I would still take them off and give them a good cleaning with a wire brush.

The second thing I would do is try a jump start. This tells you a lot, whether it starts or not. If it starts, it tells you that the problem is in your battery or alternator or starter relay or even a fuse. If it doesn't start, then it is probably something with the engine keeping the starter lugged down.

try some proper jump leads and not then cheap chinese things ,you need cables with a copper inside the diameter of your ring finger and double connectd to each side of the clip before you can even think of trying to jump a engine ,these cheap cables are only for charging one vehicle to another not passing 200 amps through