For 23 years, Houben's family felt he was locked inside his body, they just couldn't find the key.
In1983, Houben was paralyzed in a car crash. PET scanning machines did not exist and scientists couldn't detect any signs that he was conscious.
Now using a keypad to communicate Houben says, "Frustration is too small a word to describe what I felt. I screamed but no one could hear."
But new technology could hear what was going on inside Houben's head.
Three years ago, scientists scanned Rom's brain and they were surprised to see normal activity.
Dr. Steven Laureys of Belgium's Coma Science Group believes others may be suffering just like Houben.
"Our research has shown that four times out of 10, if we are not careful and don't use the appropriate measures, we can get it wrong," said Dr. Laureys.
A vegetative state is when the eyes are open and can move. The patient goes through periods of sleep and wakefulness, but remains unconscious and cannot reason or respond.
Houben was suffering from locked-in syndrome. His body was paralyzed, but his brain was alive. It's caused by traumatic brain injury or stroke.
"What happens in a lot of these cases is there's damage to the outer part of the brain. But that gets better," said ABC News Senior Health and Medical Editor Dr. Richard Besser. "And they don't do additional testing to see if there is somebody inside there that's trying to communicate that can't."
Patients diagnosed as being in a vegetative state with no hope of recovery are sometimes allowed to die, which is what happened in 2005 to Terri Schiavo. She was the Florida woman at the center of the biggest right to die case in U.S. history. Her feeding tube was removed.
Houben's family says they refused to believe doctors and felt their son did know what was happening around him.
On his keyboard Houben types out his gratefulness, "I want to enjoy my life now that people know that I am not dead."
Houben's mother is a neurologist. She was the one who insisted her son be tested with the latest brain scanning technology.
Dr. Laureys says a study conducted last year checked 103 patients in a vegetative state, and found 41 percent of them were misdiagnosed.