Tip 1: Click Start, Run, and type "msconfig"
A menu will pop up. click on "Startup" tab and uncheck everything you see there. Restart your computer and it should be faster already.
The reason why I told you to do this is because brand name computers usually come with tons of junk installed and by default it all starts when your PC starts. This slows down your system considerably if you don't have a lot of RAM. When you uncheck everything in msconfig, you are not deleting your junk. It's still there on your pc ready to use when you need it. You only prevent it from running automatically which frees up valuable system resources. ;)
Tip2: Find out how much RAM you have. If it's less than 1gig and you are using Vista, buy another gig for a total of two gigs and install it. Before you buy ram, find out what ram your computer can accept and if it can accept additional ram at all.
Tip3: Run an antivirus scan and a spyware/adware scan. Viruses ans spyware can slow down your system.
Go here for a free antivirus:
http://www.free-av.com/
Go here for free adware/spyware remover
http://www.lavasoftusa.com/
Tip3: Defragment your hard drive
Start, Run, Accessories, System tools, disk Defragmenter.
Hepe this helps! good luck!
Tip4: See how much free space you have on your hard drive
If it's less than 1gig or so, delete some of the stuff you installed, and not using. ;) When you have very little free space left the system becomes slow.