|1. Thermal paste is NOT optional. *Most* heatsinks come with a thermal pad preinstalled, if not, paste MUST be used. Here's the instructions...find your CPU & read them over:|
2. ALWAYS benchtest the main components (board, CPU, RAM, video, power supply) outside of the case to confirm they're good. Check the temp readings in the BIOS & manually configure the BIOS settings for best performance. If everything checks out, transfer only the above components into the case. After they'll installed, test them again.
3. after completing the above, install just the floppy drive & run Memtest86 to confirm the RAM is good. If you don't have a floppy drive, install just the optical drive & run Memtest86 from a CD instead.
4. if everything checks, install the rest of the components, then the OS/drivers/software.