Dimension 9200 - won't boot & makes a noise

Hello,

I'm new to the forum and I've been searching for this problem but I'm finding nothing that matches my issue exactly so before I open her up and do all the suggested things I thought I'd write a new post.

So I have a dimension 9200 and its been working fine for a few years now. But yesterday I moved house and in the process I drove up on the pavement to unload and I hit the pavement quite hard. Now I'm not sure if this story is related to the problem but I have a feeling the hit possibly broke something so I thought I'd mention it.

This is now what happens when I try to turn on my computer.

Plugging it into the socket:

1-turns on briefly as expected

2-the fan make a very loud noise and powers up (almost goes into overdrive) and shuts down.
This second part didn't happen before.

Turning the desktop on: 

1- computer makes a buzzing/whirring noise for a few seconds, then stops then again for a few seconds then stops etc.. about 5 times then silence

2- while all this is going on nothing is sent to the keyboard mouse or monitor. None of them detect anything

3-you then cannot turn the computer off using the button (either a single press or holding it for several seconds) and you have to unplug it from the wall.

I have no idea where to start with this. I fear the pavement hit might have caused this but I really hope not  :(

Please help with any suggestions. I really hope its not totally dead.

Thanks!!