PC restart Problem

Hi,

I have custom built PC.
The configuration is as follows

Processor: Core 2 Duo 6600 (2.4 Ghz)
Mobo: Intel DG965RY
Memory: 2 GB (1GB X 2)
Video: XFX 7600 GT
NO external Sound card
Sony DVDRW (IDE) is attached with a 250GB and 1TB hardrive (both SATA).

DSL modem attached to the PC through a USB. The drivers of the modem simulate a LAN port when connected.


The PC is little more than 3 years old. It was working fine till few months back when I was browsing, the PC

powered off suddenly without warning. Then when I restarted, the PC was switching off after few seconds while
Windows was loading. Whatever I do, the PC was restarting at the same point. I had a dual boot with Win Vista. Even that was behaving the same way, restarting at loading. I suspected the Mobo was bad and took it for testing. The Mobo was sent to Intel and got back with no errors.

With no other option I tried to reinstall the OS. The PC started without problems and was able to install most of the softwares and modem drivers too.I thought it was a OS issue.
But after that I am facing following problems.

1. The LAN port is not working anymore. Basically the driver is not installed. If I try installing the driver, the PC powers off (NO BOSD, only powers off). Then I have to restart and choose it boot with last known good config.

2. The Linux Live Boot from the CD is not working. It starts loading and restarts abdruptly.

3. Sometime when I start the PC, the PC does not switch on. But it turns on and then immediately its turns off and then on again... it goes on for ever. I usualy just switch the main power for sometime and then it start it again. It works fine

4. The Modem which I use for the internet, the PC stops recognising it after some time while browsing. The USB light in the modem gets switched off. I have to switch off and on the modem to get it recognised again. I think its not modem issue but my PC issue. Because after this if i try restarting the machine, it does not shut down. if restart it forcibly, it goes into the toggle mode as explained above.

90% of the time PC works fine. But sometime I face this power toggle issue and the frequncy of this happening seems to be increasing. Also not able to use the Linux is also very annoying.

Can anybody think of a reason for this problem?

Sorry for the long post. Thought I will explain the whole problem.

Thanks,
Sandeep

PSU is always an extremely likely culprit for unsolicited power off events....; mb is far less likely, but, can't rule really think about it until PSU path is checked first.

I would also try memtest when you get this thing booted and see if that works. If this is not the culprit I would try stepping down or resetting to the factory settings so your ram is working a little less. If you have an extra pci slot I would dump your current lan type setup and get a real ethernet card and plug directly to your router. The USB will limit your ability to upload and download much more than a regular ethernet setup and it shouldn't be that expensive if you have a pci slot. You can test your psu with a multi tester but if it is under 350/400 watts I would say it is dead or dying.

The 350 watt is probably ok, but it never hurts to have a little more head room when talking about PSU's. As a psu ages it will not work in an optimum fashion and parts will age causing it to not be able to produce as much power or to work less efficiently. 3 years is definetly enough time for a psu to start dying so I would consider replacing it with a good name brand 400-450w psu (you can go more if you like but the video card and parts you stated should not require much more than this) with a 5+ year warranty (almost all of the decent companies have warranties of 5 years).
You may be getting a bsod from the network set up, the best way to rule it out is to get rid of it and boot up, than see what happens. If no blue screen load in the card you have sitting around and see what happens.
As for ram timing, this is changed in the bios- the three factors to consider are the MHz at which the ram runs, the timing (usually a number like 9-9-9-24), and the voltage of the ram. Clearing the CMOS by removing the battery on your board for 10-15 seconds or so should cause the ram to reset to its factory stock setting. If you look up the ram the company should be able to tell you what these settings are. Ram can often be a culprit in having issues as ram will age quietly and there is no real warning that it is dying until something crashes and no longer works. changing the MHz of the ram and tightening the timing usually will fix issues without sacrificing performance but you should consult the ram maker for settings.