Dell Optiplex 740 Windows 7 Freezing UP

I had a similar issue on a Dell Studio computer.  Under Windows 7, it would run for a while, then the video display would start to get colored bars in it, until I rebooted.  As time went on, the problem started to get worse, causing bluescreen errors and other errors that showed up in the Windows log that the graphic driver was being restarted, especially when running Media Center.  Booted to DOS, and the thing ran great on the bench for days.  I had also tried updating video drivers and such, to no avail.

The problem eventually turned out to be a failing video card.  I replaced it with a spare I had, and the problems all went away.  Put the original one back in, and the problems continued.  Contacted Dell & replaced the video card under warranty, and it's been fine since.

As for WinXP running fine, the Aero interface takes a much harder toll on the GPU processor, so this could be simply a sign of imminent failure.

Have you tried swapping out the video card? If video goes fuzzy and then the machine freezes, I would suspect that or the drivers are the case. Since you updated the drivers, I would give that a shot.

Thanks for the answers. I just installed a new video card Nvidia Ge Force 8000 and its driver. Now the video no longer gets fuzzy but the PC just freezes. I updated the BIOS to 2.2.7 version, but still no luck. I also looked in event viewer but no errors are showing up to explain this problem.

The Power Supply unit could also be starting to go.  When the PSU is unable to keep up with power demands, it puts out less power to each component that needs it.  The power-hungry devices (video, CPU) tend to be affected first.

How old is this machine?  Do you have a comparable machine that you can use for swapping out parts?  If not, then this gets a whole lot tougher...

install speedfan, to monitor the temps : http://www.almico.com/speedfan.php
it may be overheating..

You may also want to download UBCD http://www.ultimatebootcd.com/

Boot with it. Choose Hard Drive > Diagnostics. Run a scan. In addition to the suggestions above, a failing hard drive can cause freezing. In fact, in my experience probably 80-90% of the time it is the hard drive.

Thanks again for the additional response, but nothing seems to be working. I replaced the Power Supply pack with a new one, same problem. PC kept freezing. Then I took the hard drive out and placed in another optiplex 740  PC and it works just fine. It has not crashed or frozen up after an hour but still testing it.

That is good news, I suppose.  It tells you that the OS and software is NOT responsible for the problem.  This puts the issue squarely back in the hardware component arena.  You've already tried the PSU, so we can probably discount that.  

What's left?  Motherboard?  Temperature/overheating?  Memory? CPU itself?

It looks like you have a spare Optiplex to play with -- so it's time to start swapping one set of components at a time.  Swap memory next, then CPU.  Try running the entire unit with an extra fan blowing across the MoBo and see if that helps.  Just keep going and you'll eventually find the bad component...

did you install speedfan yet?  a good first step
you can also run burnintest : http://www.passmark.com/download/index.htm
windows 7 may be loading the video card more
look also for bad capacitors  - swollen or leaking :

Thank you for all your help. I was able to resolve the issue when I set the power setttings from balanced to high performance. For some reason that works and have left the pc on overnight without it crashing.

tx for feedback - very starnge high performance works...

also not that the PS can go bad - and delivers less Max output over the years
you can calculate the power needed here : http://images10.newegg.com/BizIntell/tool/psucalc/index.html

always leave 50 W margin