Can I put my computer (tower) on its side, or does it need to stand up?
Answer: It is likely that your computer will operate normally while laying on its side. However, unless the computer's manual specifically states that it is OK to place the tower on its side, I would keep it an upright position. This is because there are a few components inside the computer that may malfunction if the computer is placed on its side.
While most of the hardware inside the computer -- the motherboard, CPU, graphics card, and memory -- are solid state parts, there are a few components that have moving parts. The hard drive, for example, is spinning at thousands of rotations every second. If the hard drive is not designed to be used at various angles, it may wear down sooner than expected. While most hard drives can be used horizontally or vertically, it is best keep them in the position they came in.
The most common problem with tilting a computer on its side is related to the optical drive. When you put a CD or DVD in your computer, it spins very fast, just like the hard disk. If the drive is not meant to be used vertically, the disc may wobble and the computer will not be able to read it correctly. You may even have problems getting the disc into the computer when it is sideways. Optical drives that can be used vertically often have small levers around the edges of the CD tray that can be pushed over the CD to hold it in place. Some slot-loading optical drives can also be used vertically (i.e. the iMac G5), but many should only be used horizontally.
Whether or not you think your CD/DVD drive supports vertical positioning, it is best to check your computer manual to see if the computer can be placed on its side. The convenience of positioning the tower horizontally certainly isn't worth the hassle of replacing a broken optical drive or hard disk.