This is indicating that the transmission computer has identified an issue and is flashing the OD light to warn you. There are many possible issues that can cause this, so it's best to have a shop perform a diagnostic check on the vehicle. If you need a shop, look for a RepairPal Certified shop near you: http://repairpal.com/volvo-within-10-miles-of-43140 Good Luck!
I agree 100% with pushrod. If there are no issues that could point to dirty injectors, then this is not needed.
Your note is contradicting itself. "Engine cranks" and "turns over" are the same thing. When you try to start it, do you hear the starter spinning the engine?
The sensor identifies when one of your lights has stopped working and turns on the brake bulb warning light. This can often be the cause of the brake lights to stop working. Check for power coming into the sensor from the brake light switch, if you don't have power, check the fuse and brake light switch. If you have power, check for power going to the brake lights. If you have power in and not out, replace the sensor. Hope that helps, good luck.
Setting the crank and cam timing requires special tools to line everything up. Did you use these? Are you getting any codes?
This requires some testing to see what the issue is. I'm not sure why you replaced the cat, but hopefully it wasn't for this issue. I would start with checking fuel pressure. These models have issues with the fuel system, so start there. Or better yet, have a professional look at this so you don't waste your money replacing parts that are not needed. Do you need help finding someone qualified to take car of this for you?
If you're going to do your own maintenance, I suggest you subscribe to one of the online repair manuals here: http://bit.ly/mitchell_repair_manuals_online And search Youtube for a few video's that show the proper way to replace a spark plug. In other words, be informed before attempting this job, these cars are not as simple as they were in the past and you can get yourself into trouble if you don't have an idea of what you need to do. Good luck.
Trying to remember, I believe it's 1-3-4-2
By clock you mean the clock display on the radio?
Your car has several computers that control all the electronics, and they all communicate with one-another on a network called the CAN, or Controlled Area Network. You should have someone that is familiar with Volvo's look at this for you, it can be one of the modules, the network itself, or even a software issue. This requires special equipment, information and knowledge to diagnose these issues, I suggest a Volvo Dealership, or Independent shops that specializes in Volvo's or European cars. There should be plenty of these around you, assuming you live in the 90210. Good Luck