What can i do so i can possibly get my desktop computer to work good as new?

I have this very old Dell Dimension 3000 Desktop that my father bought for me in 2001, It's been acting up lately it always freezes even though it has 768 MBS Of ram memory that i have install & upgraded. Everytime i'm on internet explorer surfing the internet it always freezes up causing me to loose my unsaved data. My father told me that he doesn't have enough money to get a new one, he only has money for food & house payments. What can i do so i can possibly get my desktop pc to work like brand new again ???