I've solved this too many times but let me share my personal experience. In my case I had to get HP on the chat and they told me about the updated BIOS for my machine. They also warned me about using drivers other than what they supply.
Guess what? It's locked up one time in weeks now. But I can live with that because I write C# code and it looks like my bad on that one.
How does this apply to you? Try dell.com, your service tag and see if they issued a BIOS and use their drivers for chipset, video and everything else. If that fails, talk to dell.
Worth noting is that malware and such can lead us away from the real causes (it's the malware or virus/trojan.) If this machine has torrents or more I always write it off as another malware damaged machine.
Bob
I have a Dell XPS M1210 running Windows Vista. Occasionally (though not all the time, oddly) when I try to standby or hibernate, the screen goes black, but the lights remain on and the computer won't respond to any commands, USB input, or anything else I try to do. I have to power down manually and restart.
Any suggestions on how to fix this problem? It's annoying enough that I'm considering a clean Windows 7 install, but if it's a hardware issue the problem will follow me. Thanks.

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