Q: 1998 Lexus es300. Can no engine compression mean bad computer and not engine replacement?

Purchased used last month. Noticed at start slight ticking when engine engaged, but car still drove smooth-- only at high speeds slightly rough idle. Nothing major until last week, car idle while driving became extremely rough. Wanted to shut off. Mechanic changed all six spark plugs. 1 of the 3 ignition packs, THEN checked and found there was NO compression in engine. Cab driver told me that the engines in that car hardly go bad and more than likely it is a bad computer. He said the engine can be replaced and I could still have the same problem. 1.How likely is it that the issue is the car computer. 2. What year Lexus has the same computer as mine? Mechanic had two other Lexus at the shop with similar years and can use one of the computers in it to replace mine to check. 3. Usually, does a simple computer replacement automatically fix the issue? It won't drive anymore. It's worse now than it was before sparks plug replacements. No check engine light/ previous owner unscrewed bulb.

My car has 152000 miles.
My car has an automatic transmission.