Computer freezes, hangs, crashes

I have an Acer x1700 small form factor computer, one HDD, one DVDRW, E2200 CPU, with 4 gigs of ram. Add on video card and sound card.
Simply put, it freezes. When it happens screen stays on just the way it was, but mouse and keyboard have no effect. Only way to shut it down is by holding power button for ten seconds. Was doing in once or twice a day and got worse and worse. I have run Avast antivirus, Superantispyware, Kapersky plus Windows Defender. Found a few adware, but nothing serious. No rootkey virus at all. Thought it might be memory or bad hard drive. Tested everything with Passmark. No problems. Pulled out one stick of memory, but still froze. Replace and pulled out second stick but still froze. Although chkdsk showed not problems, I thought it might be something really bad on HDD, such as MBR, so I actually pulled out the hard drive, inserted a new 500GB Seagate, and reloaded Windows Vista from scratch. Never got through loading up before computer froze again. Could never get it to stay on long enough to run the updates for Windows Vista, so I pulled the HDD and replaced it with the old one. Still hangs up. Now, it hangs within 10 seconds of Windows starting. I thought maybe heat was a problem but I left computer unplugged for hours, turned it on, and crashed immediately on startup. Every hardware test I try to run shows no problem. Except for video memory, and that was because I did not have DirectX running. Could not reinstall it since I cannot get computer to run long enough to do it. What is really strange is that it will run a long time in Safe Mode. Sometimes 10 or 15 minutes, but still eventually hangs. Save Mode with Networking not so good. Better than normal startup but still hangs. I thought it had to be a software problem because I could not understand why it would run in safe mode but not normal unless it was software. Replacing HDD pretty much ruled out software unless someone has a better idea. I pulled the add on cards and just ran from the onboard video. No difference.
It has been a great little machine, and my wife loved it. Probably not worth replacing CPU and motherboard but I don't know how to rule them out without replacing them.
Any ideas would be appreciated.

 

Have you checked the CMOS battery? It's usually a CR2032 3V.
You've checked everything excluding the motherboard/CPU which is probably where the problem is. One option is to load a bootable Linux disc. In the BIOS, set the first bootable device to CD/DVD drive. You can also press F12 (usually) while booting and select CD/DVD drive.

 

Just an update. I appreciate the input. Replaced the CMOS battery but did not change anything. Still freezes. I finally tried another CPU, but still froze, so I purchased a replacement motherboard. Works like a charm now. Took a hard look at the old motherboard and noticed that several of the capacitors were no longer flat on top. Rounded tops, so I figure that was probably the problem. I never could get the burn in tests to recognize my graphics, even with graphics on the board turned off and a separate graphics card installed. That was the only error I ever found and don't understand why the graphics card would not work if the motherboard video was bad. I have tried the graphics board on the new motherboard and it works fine.
Anyway, the motherboard solved the problem and the system is running fine.
Thanks!

 

Pass it on to everybody you know with this problem. I just found the answer last night. Go into your browser(s) and DISABLE JAVA. That will change everything and Windows 7 speedup will amaze you. There will be no more hang-ups or slowdowns when your computer is idle and you start up again. It is amazing! I couldn't believe the difference.

NOTE: JAVA is different than Javascript. The average person, does not need JAVA on his/her hard drives at all. Try it, then thank me.

 

Thanks, Claowl, but I have already replaced the Motherboard and CPU. Everything is working fine now. I don't think mine was a software issue. Had something bad wrong in the display area of the motherboard or the CPU.