My computer locks up with the last sound played again and...

I´m using Win98SE and usually play games and downloading different things on the internet. The problem ( which is a really BIG and irritating problem ) is that the computer locks up without any reason with the last sound played again, and again, and again...and I try countless many programs to get it out of the way, but it never dissappear!! Now, if anyone have met this problem before and know exactly how to fix it, well, I don´t know how to thank you...