HOUSTON -- Note: The following story is a verbatim transcript of an Investigators story that aired on Monday, Sept. 8, 2008, on KPRC Local 2 at 10 p.m.

Local 2 investigates computer repair companies. Hard drives, software, mega pixels and gigabytes -- when it comes to computers, many are clueless about what makes them run.

But how much do the computer professionals you pay really know?

In tonight's hidden camera investigation, investigative reporter Amy Davis took a desktop computer to one repair shop after another to find out who's repairing your computer and who's just cleaning out your wallet.

Dan Wallach tinkers and teaches at Rice University's Computer Security Lab as an associate professor; but when it comes to computers you might call him "Nerd, geek, something like that," Wallach said, finishing the sentence.

To family and friends, Wallach is "Mr. Fix-it," but we asked him to fix our computer so it would not work.

"I'm just gonna put it on kind of half-hazard," said Wallach pulling on a cable to the hard drive.

We took the computer in for repairs all over the Houston area to find out one thing.

"I'd like to know if you could tell me what's wrong with it," Davis asked a technician with a hidden camera rolling.

"Just like I don't really know how to fix a car, a whole lot of people don't really know how to fix a computer," Wallach said.

College junior George Morrison is one of those people.

"It was running a little slow," Morrison said about his laptop. "I was worried it was our Internet connection."

Morrison took his laptop in for a check-up. When he got it back, it wouldn't boot up at all.

"We rely on the people who do that not to rip us off," Morrison said.

So, what would computer technicians tell us?

We called on five companies, using BBB complaints to select the businesses.

We made appointments for two companies to come to the house. But, first we took our computer to Best Buy's Geek Squad and Circuit City's Firedog.

"It just stopped booting up right," our employee explained to the technician behind the counter.

Remember -- we know what's wrong. The computer won't boot up because we loosened the cable to the computer's hard drive.

"The fix for this computer is easy. Push it back in," Wallach said.

Back at Best Buy, it took a Geek Squad tech 36 minutes to properly diagnose the problem. He did it while I waited and for no charge.

At Circuit City's Firedog, it wasn't that fast and it wasn't free.

"It's $59.99," the Firedog technician told our employee.

"$59.99, just do to a diagnostic?" the employee asked.

"Yes, ma'am," he replied.

"I mean, if you turn it on, you'll see what it's doing," the KPRC employee said. "That might tell you right away what the problem is."

"Well, I mean, it'll show me what the problem is, but you know it could be a hard drive, it could be a mother board, it could be different types of things," the technician said.

So, we left the computer overnight. Firedog called us the next day. Technicians found and fixed the loose cable by pushing it in. With tax, it cost us just under $65.

Skypot Computer Center on Bissonnet checked out our computer for free.

An employee wrote out what it would cost us to fix it -- $269.95 was Skypot’s cost to install a new operating system.

When we went back to the store to talk with the tech about the diagnosis, he hid in the back and refused to come out and talk.

The store's owner sent us a letter, saying his shop would never have made the recommendation we got in writing. He even doubts we took the computer to his business, even though it's all on camera. You can read the letter in its entirety by clicking here.

We scheduled a house call with The Computer Clinic in Katy so we could see exactly how the tech diagnosed our problem.

In 10 minutes, without ever removing the computer's cover, he told us this.

"So it looks like your drive is probably … looks like it's gone," said The Computer Clinic tech on hidden camera.

"So what do you recommend?" the KPRC employee asked him.

"I would recommend that we put an operating system on here so you can get it running," the technician said.

The diagnosis cost us $70. The tech told us the new operating system would come to $243.63.

"Did you ever think about checking any cables? Maybe it's just a loose cable," Davis asked the technician on his way out of the house.

"Uh, we didn't. I didn't look in there because I figured whenever it says there's nothing coming up, that's it. Unless maybe it does. I can look at it right now," the repairman offered.

The Computer Clinic said they would have noticed the loose cable once they got our computer to the shop. They said we wouldn't have been charged for the operating system we didn't need.

The computer technician for Bits & Bytes was in the house for just four minutes when he spotted the problem.

"So far from what I’ve seen, the hard drive cable here wasn't pushed down all the way," said technician Derrek Labrosse.

Bits & Bytes charges by the hour. Our repair cost us $81.

"Well, it's an hour, so if you want me to stick around," Labrosse offered.

So how do you know who to trust? Just like shopping for a car mechanic, you have to shop around.

Check complaints with the Better Business Bureau and make sure you tell the shop not to do any work until you approve the charges.

If the diagnosis is free, take your computer to a couple of businesses to find out if the diagnosis is the same.