A lot of our customers know about this, but I thought I'd put it out there for everyone. It's important that cold computers be given a chance to warm up before use. Even though the majority of a computer's internal workings like the cold, there are some moving parts that don't do well with it. Hard drives and fans being the best examples.
How cold is "cold?" It's hard to put a fixed temperature on it, but consider room temperature to be an appropriate point to turn your computer on. Anything under 50 degrees and you could be reducing the life of your computer. If you've left it in the car overnight, it takes several hours to warm up fully.
If you need to get your computer on quickly after leaving it overnight in the car, open it up as best you can and put it in a warm area with a fan pointed at it. If your computer is a desktop, remove the side panel if you can. Any amount of warm air circulating will help things. Of course, your computer should be off and unplugged during all of this. If you have a laptop, take out the battery.
You'll know the computer is ready to be turned on when the external surfaces all feel warm. Due to the risk of static discharge, I suggest against feeling inside the computer.