need help with my computer

Ok i am not good with computers so please don't explain in really difficult languages thanks^^.
So my computer used to run perfectly when i first got it which was like 3-4 years ago and now it is like real slow when i open my firefox, and my other programs but it is not my programs that is slow too it is also "My Computer" and "My Documents''. and i tried everything that i can think of to make it slower and it still didn't make a difference.
The methods i tried was scan my whole computer with avg 8.0, deleted unwanted games, delete some files, reinstall my firefox.

The CPU and amount of RAM i have is
Intel(R) Pentium(R) 4 CPU 2.80GHz
2.80GHz, 1.00 GB of RAM
A7600GT
can't remember what is my motherboard model so yeah

Please help me

http://www.auslogics.com/en/
quick defragger,,really....
go here dig around a bit and download their free defragger,it will only defrag not sort,that you can do with something else,once you have defragged consider a reinstall right over,sometimes it does wonders,of course nothing beats a format and reinstall and ,regular use of of a good reliable back up proggie ....

This is a neat tool that is free and has several functions to optimize your system.

http://www.glaryutilities.com/

Theres a 1 click option to do several fixes at once. Theres also other options if you search around and you will find a registry cleaner and a defragmenter program that works nicely.

Run an antivirus and spyware program to try and pick up and clean out any infections prior to giving up to reformat and reinstall your OS and programs.

If all else fails, reformatting and installing everything fresh will fix the problem as long as there are no hardware issues...

$50 fix:

By a second hard drive and move the default my document location to the new drive.
Then defrag the c: drive.

I just did this to an old HP computer with similar spec's and it helped a lot. For even better performance, do a fresh install.