fixing wifes desktop.

My wife has had her hp desktop for two years now and she almost never turns it off. Well this has taken it's toll, it runs slower, when booting up it goes to a black screen that checks the files in the HDD and it makes more noise the a old Ford Fiesta. To fix the problem I was thinking about doing three things, Some of the noise is coming from her fan so I want to replace that (dont know which one to get), get a new HDD (putting windows 7 on it) and getting can air to spray all the dust out of it. Do you guys think that should fix her problems and I know newegg.com is the place to go but what fan do I buy and does it matter what HDD I get. The HDD I am looking at is a
1TB for 89.99$. Any thoughts would be appreciated, Thanks.

Sounds like it needs a fresh install on a new HDD, yes. Ensure that your wife's PC has SATA ports on its motherboard (or that the old HDD is a SATA one) before you go ahead and buy a new HDD, as almost all new ones are SATA as opposed to IDE.

Edit: If the noise is bothering you, try putting in a new low decibel fan from Newegg, too. You could even go crazy and get her an LED one

Unless she plans on storing huge amounts of files, which i don't recommend(hard drives can fail at any time), she won't need a huge drive. If you don't know whats making the noise, you need to take the side cover off the computer and listen to see what is actually making the noise. Not sure what fan to get? Take the bad one to a local computer shop and have them tell you what size it is.

The black screen that comes up, are you sure its not a 3rd party program that was installed to test the computer at certain times? You may want to download the hard drive makers disk diagnostic utility and scan the drive for errors. It may be on its way out and if you have data on it you need saved, you need to quit using it until you get a new drive to back it up.