Lockups on my new rig

[mmmstew]

I've built this pc back in march now I'm getting black screen lockup's when I return to the pc after hours at a time.Just wondering where I should start to troubleshoot,I have a 550 watt psu a 8800gt 2 gigs ddr2 in dual channel slots, with a m2n sli deluxe board,a dvd rom and 2 hardrives one sata 250 gig and one in ide 60 gig, and a x2 6400+. Now I'm gonna mention nothing is currently overclocked and the pc has been working great when I am on it. Ie playing crysis,oblivion,tf2,hellgate, etc etc. Almost all the latest great games. I'm thinking it may be a video card problem possibly poor driver i'm currently using 174.74.
Any positive feedback is greatly appreciated and I also wanna note hardwarecanucks is a great site and I'm happy to be a member,and all you friendly people on the forums have been very helpful in the past =)

[sswilson]

Are you overclocked at all? What's the make/model of that 550W PSU?

[tzetsin]

If i'm understanding you correctly, your saying your computer is going on standby or hibernate while your away from the pc ,then wont come back on when you return?

How long has this been happening? could you possibly do a system restore to a time you know for sure that it didnt happen? system restores are reversable so they're a good tool for finding out if its a software issue.

[mmmstew]

this is my psu and no I'm not overclocking
Ultra Products - LSP (Lifetime Series Pro) 550-Watt ATX Power Supply

[mmmstew]

It's not hibernating cause I do not have it set to, and it's not on a battery like a laptop =p, also It's just going into standby but won't return come back on,but sometimes it doesn't do it it's just wierd and as far as system restore goes I never use it to avoid certain malwares backing it self up and being able to remove it easier.Not that I'm always getting viruses or spyware just I like being able to remove em quickly.

[tzetsin]

My guess is its a software issue, as long the computer is running perfectly normal otherwise. turn off standby and set your monitor to screensaver a black screen, see if the problem stops.

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[mmmstew]

I decided to look around and changed some settings,I removed my screensaver and set the moniter to turn off in 2 hours. I've also overclocked my video card again and surprisingly things have been running better.clock speed are core clock 700 shader clock 1750 and memory clock 1000(which is basically 2000). These speeds are the speeds on ssc model.I just have a 8800gt evga 512mb and have my fan maxed. With a bit of ocing.
Havn't returned to a non responding screen in days thanks for the input people =)