Q. Are those do it yourself online computer tarot readings valid?
A. It depends on what you mean by "valid". The answer could be yes or no, depending on how you look at readings in general.
If by "valid" you mean "accurate predictions", then the answer is no. The computer readings can't read minds, tell what is in someone else's heart, or predict what others will choose or what will happen any better than a human reader can.
When you get right down to it, tarot cards are just a tool. The important thing isn't those little pieces of cardboard with the pretty pictures...the important thing is the spirit of the person looking at them. Whether that person is you...or someone else looking on your behalf...tarot cards, palm lines, tea leaves, rune stones or what-have-you are all just tools...a spring-board that helps us access the intuition within. That intuition, in turn, is guidance, not predictions. Long story short: Tarot cards, no matter whether they are paper or electronic, are just a way to help us solve problems and make better choices. Those choices in turn create a better future, rather than predict some imposed fate outside of ourselves.
In that way of looking at things, then yes, electronic tarot "DIY" readings are just as valid as if you drew physical cards for yourself. Either way, paper or virtual, the cards are just a spark to help you access your own inner wisdom, understanding and intuition.