Check your ram. It could be a bad stick or two... You might try pulling one, running your PC and the try the other. If you have only one stick, now is as good a time as any to upgrade. At the bottom of the main page you will find a link to crucial.com
Use it, look up your model and the maximum amount you can install. Then buy an extra stick. So if you have 256Mb and you want to upgrade, (as long as your model permits) get an extra stick of 256MB, totalling 512Mb. When the ram comes, try the new ram by itself. See if you get the IRQ error. If not, then try both sticks, if after you get the IRQ error then you know it was a bad stick of ram...

That could be the issue..
Also, you might want to try doing a system restore using start, all programs, accessories, system tools, system restore...
and restore it to a date before you installed NAV, Zone Alarm etc...
WIth regards to reg cleaner as Conan mentioned above, make sure to do the following.
Just open reg cleaner look for any reg entries labeled zone alarm, symantec, or norton, live update etc... and remove them. then restart and try your PC again...
That may help as well.
Good luck and welcome to TZ.
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