Any small fault (intermittent is the worst) on the main components can be very difficult to track down.
The easiest way (after the usual testing) is to swap out components but, not always possible.
A small fault in two or more components can be exasperating at best.
Good RAM info on the SPD tabs, unusual to get two different RAM brands with the exact same SPD specs.
Crucial (Micron) is a RAM manufacturer, they probably sold this to PNY.
The low voltage RAM may not be stable in this motherboard.
For testing let's bump the DRAM voltage to 1.600v and the NB voltage to 1.300v.
I wouldn't think the SSD is causing any stress on your system, should actually lower the system power load.
It might be stressing the RAM due to the speed of the SSD.
Is the Crucial RAM you are using now single or double sided?
This is important due to RAM card chip size, double sided has more, smaller sized chips. The NB can only handle the smaller memory chips.
This may be a factor, just for testing (single or double) pull the Crucial RAM and let's see if it is more stable.
The PNY RAM cards should be in slots 1&3.
Then swap the PNY for the Crucial, if the Crucial is double sided.
Have you Clean installed Windows 7?
If yes, how many times and when was the last time.
A quick search shows a lot of RAM issues with this motherboard, seems to be a bit touchy with settings.
There are a couple of approaches to check this, bump DRAM and NB voltages and/or loosen the frequency and timings.
Is your DRAM timing Mode on auto (SPD settings enabled)?
Motherboard faults are the hardest to find, usually need to confirm every other component is functioning correctly, which can be 100% confirmed by testing your other components on another motherboard.
Your PSU is made by Delta Electronics and gives max 12v load of 540W. PSU REVIEW DATABASE
How long have you had this?
They do degrade with time.
The above link is a good reference, I prefer PSU OEM Seasonic, they have an excellent reputation and track record.
Antec is also a well respected brand, as is Corsair but I still had a Corsair PSU fail in less than a year.
When a PSU fails it can be a slow drawn out process causing all kinds of errors/faults/crashes, in the worst case it can take other components out with it.
GPUs are another huge variable, the GTS 450 series does have a reputation of not being the most stable nVidia product.
Again, swapping to another GPU for testing, or putting your GPU in another system, is the easiest way to confirm.
It's a good thing we like computers, they can be a lot of fun and sometimes not.