I don't recommend using a vacume cleaner hose (or floor type roller) inside a PC - the suction isn't great for the dust that can be caked to the electronics. You might have bumped into a part and damaged it - I doubt static electricity was the cause unless your hose was metal.
In the future, I recommend a can of AIR (About $3-5 a can) which can do it safely. Sometimes I use an air-compressor (friends) - but it maybe possible to damage with that because of the extreme pressure, but it does do the best job for dirty computers.
If the mobo is fried - your data is still GOOD, but you'll need to replace the mobo (which may require another winxp key) and install windows on another drive - then xfer the data from the original drive to the new drive.
But lets try to see if its DEAD DEAD... Locate a jumper on that mobo, it should have 3 pins in which 2 are covered. Switch position with power plugged in, but not ON. Let it sit for about 10secs - then put in original position. With RAM/CPU and MONITOR plugged in - see if it lives. (Monitor is NOT keeping the system from booting - if its using the onboard video) - remember, NO DRIVES or extra cards attached.
If still dead -Pull RAM & CPU(unplug power) - repeat jumper thing - then power it up WITHOUT CPU&RAM for about 5 seconds. Unplug power - reinsert CPU&RAM and power up. Yeah it SEEMS strange, but I have recovered more than a few computers this way.
If dead... you have a girlfriend to please.
The motherboard on ebay goes for about $10 - but it needs to be available.
You could also go to Frys or newegg and get P4 board (Socket 478) which will cost about $140~150. But we also don't know what else is damaged... RAM, PSU (doubt - unless you vacumed with the power on) or CPU.
And youre kind of throwing good money after bad (unless you can test things out) - but the remaing parts are good (HD, DVD drive). So you may end up spending $200~300 trying to replace any bad parts.
So ya may look at getting a new computer or building a new one...
Here's a Compaq for $400 and would SMOKE that emachine
For $100 more, doublethe ram to 1GB, 250GB HD and card slots: