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4096 to 3069 is a big decrease at 1024mb per gb, you lost 1 of your ram modules. It is almost exactly 1 gb if you use the actual 1024 mb per gb (no it is not 1,000).

I suggest that you take the memtest86. Run for 8 passes and then take a good stick and test each slot for 4-8 passes.
Guide to using Memtest86+

The numbers very clearly indicate it is one stick. You do the math.The difference betwen 4096 and 3069 works out to 1027 too close to 1024 to be a conincidence.

If through your own research or for other reasons you believe that there may be other causes, start with the test, then you could move on. I feel that you will find the reason with that test.

In addition, if you decide to replace a bad stick, replace all. Yes, I know about sites like crucial where you can get an exact match etc. Again,, dont mix and match.

I hope that I am wrong too, but the evidence points toward one stick with a problem or worse the motherboard.

In my earlier post I gave you the official memtest document. Now Ill give you one that may help a bit more
Guide to using Memtest86+

In your case, what you can do, in addition, is take out one module, does it change your Physical Memory, yes, then that stick is good. When you take one out and phyical memory does not change that is the bad ram.

If you want precise results, dont skip steps. Make at least 8 passes and check the individual slots.
That being said, if your only problem is the amount that is shown on task manager, does not really make that much difference as it does not affect you.
Be sure that all your stuff is backed up, just in case.

I know your anxious, but take your time. If you rush and get the wrong results, we may never find the true cause.