More things that can make your computer very slow, check your BIOS setup.
Check your CPU and memory bus speed and see if are at normal value for your CPU model, motherboard and memory. Sometimes all is running at low speeds.
Check your power management, your computer can be hybernating every moment.
Check the hard disk is in 32 bit mode and Ultra DMA enabled.
Next thing to check is how are running your disks, go to control panel - system - hardware -device manager - IDE ATA controller - Promary/secundary channels, click on properties -Advanced sertings and see if is using ULTRA DMA 5 or 6, for CDROM can be lower. If you find the is using PIO mode you are damned and your disk turns very slow.
The only way to correct this mess is uninstall the IDE channel driver and restart your computer.

Stupidity also evolves!