Sorry to take so long getting back to you. I feel your pain and I hope you can work things out.

Did you mean that when you attempt starting the car that its completely dead. Like nothing, no dash lights, no signals, no nothing? If That is the case, thats extraordinary. And you could be waterlogged somewhere. Your car is powered , via the battery through a terminal clearly visible on the driverside fender, in the front(square black box). Could be some loose wires, are corrosion. Very possible after 24 years(congrats). And could cause your intermittent symptoms. Moisture and corrosion work well together to cause mayhem.

If you get everything except the starter, then something is preventing current flow in the starting system. I have washed my volvos engines many times without ill effect. But Ive found, over the years, many corroded and bad wiring connections that cause the same problems.
Usually the problems are not major and are easily fixed with some new wires, tape, and a little mechanical skill.

Whatever it turns out to be, I hope its not to painful, and that brick is soon back on the road, and your headache is over. Good luck.

If you are going to continue owning the volvo, don't give up on this web cite, there is a lot of information available here. Ive saved lots of cash over the years because of this cite.

Also, please let us know what it turns out to be.

Another suggestion, if you havent already, use the search window at the top and look for more information.

Good luck