Hm, assuming we're talking brand new installed Win7...
Beware that on default settings after installation, Win7 schedules energy saving/hibernation after 30 Minutes of no user activity. That needs to be manually disabled.
Also, only use WHQL/Release Drivers for your cards, AMD's Beta Drivers often focus only on specific game improvements, while sometimes having less than stellar stability for other applications.
Other than that, I've seen cases where plugging the System simply into another (not co-located) Power Plug, ideally running off another fuse in your house electrics, actually helped.
While other, typical devices may work without issues, such a System with relatively high PSU load and requirement for binary accuracy may not take even smaller power surges (which are normal) without effect.
PSUs vary in quality concerning surge tolerance and the time their internal capacitors can stabilize surging power input.
I remember running alot of rigs (long before bitcoin era) off several Multi-Plugs connected to different power plugs w/ extension cords - that I thought was a good load distribution.
One day however I discovered that alot of these plugs I used in different rooms were actually fed by one power line going to a single 16A fuse in my house, which simply was under very high load @ full operations.
Powering up the rigs too fast in a row or throwing the switch on one of the Multi-Plugs to ON with PSU power switches all in ON often caused a pretty good initial peak load with expected results
Powering some on or off within that setup also caused other systems to lock up sometimes.
Mystery was only solved when that single Fuse kicked in and I realized above. After changing the electrical distribution by feeding half the computer fleet through their own line with own fuse, these problems vanished (after months of searching for the otherwise inexplainable cause).
It's also possible in theory that other high-level comsumption devices are kicking in/out and cause a short general power surge in your house (enough to freak out a loaded computer PSU), if the electrical wiring setup of it isn't well done (large refrigerators or electrical stoves are known to do that, 2000W+ blow-dryers or heaters could also easily do it depending on which electrical wires they operate at; if they share the same line/fuse that your rig is running on, that's a good possible reason for issues).
If you still have classic light bulbs in your house, seeing them change intensity periodically or at random is often a good indicator of such issues.
