Hmm, what exactly do you mean by won't turn on? Does pressing the power button not do anything at all? If so it's likely a fault with the battery, and if it persists even when plugged in with the battery removed then it's some hardware failure in the power circuitry. Either that or the power brick went bad at the same time as the battery. If it is a hardware failure not related to the battery or power brick then yeah, that could be a problem on a laptop. On a desktop you could just replace the PSU... To be safe try removing the battery and running it from a different wall outlet than you normally charge it on (preferably in a different room of the house as well). If you have access to a second power brick/cable try that too. You can never know...
If it does turn on at all but the POST screen gives some sort of drive error, than obviously something happened to the drive. Likely corruption of some kind, perhaps due to age. At the best it'd merely be a problem with the MBR or partition table, at the worst it could be a head crash. Now if the POST screen gives some sort of other error it could be anything from a dead BIOS battery, corrupted BIOS chip, or some other random hardware failure that may or may not be easily solvable depending on what exactly failed.
On Firefox, I'm assuming your dad doesn't want you to install anything on the computer but if you need FF (which you do. IE sucks. Really) go get Portable Firefox. It's entirely self-contained, being meant to run off a flash drive. No trace on the computer at all, no registry settings, cookies, history, cache, nothing. Well, unless you run it off the computer but you can just delete it afterwards if that's the case. No uninstall needed!
That's given me an idea. Perhaps we can have a bit of a challenge, that whoever can write a small story or something to that affect, of a messed up person, ummm get's the honour of realism?
I pretty much already have. Again, though, they can't be posted here.
...Okay, actually these ones aren't that bad as they don't have any, you know, pr0n or anything in them but they are still fetish writing which I'm pretty sure would be breaking the rules even without the pr0n.
God, I'm like the FFL perv or something.