CPU gone bad?

I would lean more to the memory being the problem TGP.

Pull a stick of memory out of the board when turned off.
Have a quick look at the timing values and the voltage for both standard mode that should be about 1.5v
And with XMP enabled in the bios 1.55v to 1.65v.

Check in the bios that what is setup is correct to what the memory sticker states, in respect to memory timings and voltage.

There is a quick test you can do while in your bios, and the memory section, voltage section.
First set the option to manually set the memory up other than auto detection by the bios.

Select a slightly lower memory frequency. Save the setting in the bios and test to see if the system becomes stable.

If you find it does.
Then it can indicate that when the memory is running at the Xmp rated 1600Mhz speed.
That cause can be due to a slight lack of voltage being fed to the ram, or memory modules.

What you do then if the motherboard has the ability to change the memory or ram stick voltages is to select manual setup. raise the voltage of the Ram modules supplied from the motherboard by a slight amount.
About 0.250Mv milli volts.

Set the Speed of the ram modules back to the Xmp rating.
That should be 800Mhz in the frequency selection, don`t forget it`s DDR 3 memory so the base setting or frequency set is always times two.

800 x 2 = 1600Mhz effective frequency, XMP mode.

Save the settings before you exit the bios again.
And see if the addition of the 0.250Mv stabilizes the system and boots into windows without any lagging, system freezing or reset of your system.

The only other symptom of what you say is lagging would be that your cpu in the system is getting very hot.
If it does, then the motherboard will be down clocking the speed of the cpu in an effort to keep it cool and to stop any damage to it
TGP, so it would suggest that you check the cpu cooler is firmly attached to the cpu socket, the fan is working on it.
That the heat sink under the fan is not blocked with a thick matte of dust. or that removal of the cpu cooler and a clean of the old thermal paste should be done, and some new thermal cpu paste applied to it then fitted back onto your motherboard.

In any case it is one of the problems to check, as it can cause all, if not most of the problems you are talking about TGP with your system at the moment.

NB: if the system has an INTEL stock cpu cooler on it.
Then the cause can also be that the push pins on the cooler are not properly latched to the underside of the motherboard.
Creating a lift of the cpu cooler in one corner.

Unlock Pins, push each down Top left, Bottom right, bottom left, top right.
Listen for any clicking when pushing down.

If you hear any it`s a lift on the intel cpu cooler.
Lock the pins off if they use the twist lock.