Lag on my brother's pc when downloading stuff.

I am currently downloading Team Fortress 2 on steam and my brother's pc is freazing up.

How can i fix this.

P.S. If this is in the wrong section please move it.

Hello ej and welcome to Seven Forums.

Have you tried downloading TF2 on another computer to see if it also lags or freezes? If it does it could be a problem with the download site rather than the computer.

Other factors that could affect the download include how much memory is installed (2GB RAM is considered the minimum for Windows 7 with 4GB being the sweet spot), hard drive problems like bad sectors, failing HD, etc., malware on the machine, and a whole lot more.

Here's a tutorial that covers how to optimize Windows 7. Some of the suggestions may not apply to your brother's machine but others will.

Optimize Windows 7

And another Forum member created this checklist of maintenance tasks that should help any computer. Heed his warning about NOT using registry cleaners.

Suggestions for Proper Maintenance

I should have been more clear, I was in a hurry sorry.
My brother and I share a room.
We are literally 2ft away from each other.
It only lags his pc if I'm downloading something with my pc.
Everything starts lagging even his games.
As soon as my download stops he stops lagging.

I have no idea why this works.
My guess is his pc is transforming internet speed into cpu usage??
No idea but I need this fixed ASAP.
(otherwise he might just kill me :P)