Alienware Aurora running extremely slow!

Alright so I got my Alienware close to a year ago and it came with BIOs A03. I don't know much about computer software or hardware so bare with me please. I played games on it just fine from the very beginning. It was super fast and had great graphics. Something I noticed from the beginning was that once I boot the computer up and it starts windows it stars very slowly to where I can't touch anything for a good 5 minutes before it loads up and I'm able to start using the programs. I don't have very much installed on the computer really. But for about the past two months my computer has started to run very slowly and i havnt been able to play any games. I can start a game up but the computer shuts itself off about 4 minutes in. It will be leggy the whole time but when it shuts down the noise sounds like a record player getting stuck and its horrible. But also before it shuts down the sound won't be normal on the game. Like mid sound effect it will like pixel the sound I guess you could say. So yesterday I went and bought compressed air and cleaned the computer to perfection on the inside because someone suggested it could be getting to hot from dust being built up. There was a ton of dust but I got it all out. Sadly it still didn't help anything and my computer still sounds like a her when its turned on. If I turn the computer on and just let it sit without opening anything the fans will kick up super loud and stay at that rate until it shuts itself off. So I don't think it's overheating if I'm not even doing anything and the fans are doing this. I also updated the BIOs to A11 so I figured that would help a ton because I still had never updated it from when I got it because I didn't know it needed that. I thought the computer updated all of its stuff automatically. But now after putting the A 11 on here my computer is actually slower and I can perform nothing on t besides start it up and look at the desktop icons. Please help me. I spent $1700 on this computer so I could finally have a good computer and play some games and have fun and still be able to do other things like browse the Internet. I have has MacaFee installed the entire time I've had the computer so it's been protected so I just don't know what to do.