OS(2000Pro) freezes very often

Recently, I received a virus,then my computer can’t even bootup. Re-format it is my only choose. After delete partition, recreate partition and format it to FAT32, my computer freeze oftenly when I use Internet Explorer. I throught once I reformat the computer, everything very reset. Can anyone give me a idea what’s going on, and some solutions to my problem. Appreciate any suggestions, thanks!