RE: PC won't boot
Sounds like some kind of a motherboard problem, although I also wouldn't rule out the power supply just yet.
Unfortunately, the best advice I can give you is to try swapping out the power supply if you can borrow one from another machine of your own (or even friend's). I'd start there because a power supply swap is much easier, even though what you describe sounds more like a bad motherboard.
If the power supply doesn't change anything, your choices will depend on whether this is a custom designed major OEM computer (Dell, HP and similar) or one built from standard components.
In major OEM designs, the motherboard is usually hard to replace with anything generic, but there tends to be a good supply of replacement parts. You would want to weigh the cost of that against basically replacing the computer.
If it's a computer built out of generic components and it is two years old, your best option usually would be a motherboard/CPU/RAM upgrade. At only two years and depending what you choose to upgrade to, it's possible that even the RAM could be reused.