The CMOS battery should be around 3v DC. 3.5v sounds a little high, but this is probably because the battery is old. The battery is very inexpensive to replace, so it might be worth it. Usually type 2032 (CR2032) is what you need, so check the battery and get the correct replacement.
The processor is usually fairly hard to get out. It is under the heatsink, so you have to unscrew that to get at it. Don't worry about the processor now, though, we will get to it if necessary.
The capacitors can leak if they are using the old electrolytic type rather than the new aluminum capacitors. The newer ones are very stable, but the older ones can leak over time.
Here is a picture of a newer capacitor:
And here is an older one which can leak:
Quickly inspect all the capacitors you see for leakage if they are the old type. I will get a picture of a leaking capacitor in my next post, along with the rest of my reply.