So my windows 10 pc has in the last several weeks started to do bizarre things, like mouse movement slows, clicking on things just does nothing until a couple of seconds and I occasionally will get a random screen blackout , then windows telling me the video drivers have failed, and the Microsoft generic video drivers have been loaded. Then a reboot later, everythings back to OK for a few days...I have the latest video drivers, an NVIDIA GeForce 8400GS which I bought at bestbuy about a year ago. The motherboard is about 4 or 5 years old, an Asus P7P55D LE, CPU an intel i5 quad core at 2.667ghz is ...I upped my system memory to 16 gigs about a year ago too. As I'm typing this, there are occasional 'stops' where nothing types out lol...Task Manager shows nothing taxing anything. So I go to the NVidia forum and one guy tells me the card is crap and everything I have is outdated and video card and probably mobo won't work well for windows 10 since their older and also that the GPU on the video card is probably shot lol...I'm sure to a gamer it probably looks very long in the tooth, but it has served me OK...I won't say well, because windows throut all versions have caused me a long list of headaches, anyway, to get this latest headache fixed, I'm hopeful I can get a different video card but I'm worried the age of the mobo may have made it too old to work optimally with windows 10, so with that in mind, what mobo + video card combo do people here recommend for windows 10? Thanks.

Well that could be just about anything. 
 
Run MemTest86.  A bad RAM stick could cause weird problems.
 
Then check drivers.  I would make sure I have the latest drivers from the original hardware sources installed, and be sure that they are Win 10 compatible (i.e. motherboard, video, audio, network, etc...)
 
Your mobo does not appear to support integrated video, so you may want to try another video card in case that one is crapping out.
 
If that doesn't work, maybe try a disk wipe and clean install of Windows, before investing in new hardware.
 
And since that chipset was released in 2009, you may want to consider rolling back to Windows 7.
 
If you are determined to upgrade, any current generation CPU/mobo should be Win 10 certified.  And I would add that the integrated Intel HD graphics is good enough for DAW use.  The 2D performance is very good, but lags behind in 3D.  So no discrete video card required, unless you want to game also.

abacab
Well that could be just about anything. 
 
Run MemTest86.  A bad RAM stick could cause weird problems.
 
Then check drivers.  I would make sure I have the latest drivers from the original hardware sources installed, and be sure that they are Win 10 compatible (i.e. motherboard, video, audio, network, etc...)
 
Your mobo does not appear to support integrated video, so you may want to try another video card in case that one is crapping out.
 
If that doesn't work, maybe try a disk wipe and clean install of Windows, before investing in new hardware.
 
And since that chipset was released in 2009, you may want to consider rolling back to Windows 7.
 
If you are determined to upgrade, any current generation CPU/mobo should be Win 10 certified.  And I would add that the integrated Intel HD graphics is good enough for DAW use.  The 2D performance is very good, but lags behind in 3D.  So no discrete video card required, unless you want to game also.

 
Yea, the frustrating part about windows is, for all of it's bells and whistles, sometimes problems you experience it literally hasn't a clue how to tell you what is causing the issue and that's with all the many and detailed apps that TRY to tell you whats going on with your pc that it does have lol...I'm definitely sticking with windows 10 though and not going back to 7 for several reasons...I'll look into a new mobo. I have run memtest and it always tests OK.

One of the problems, just "replace the motherboard" probably will also require new CPU and Memory, as current technology boards (most) are not backward compatible with CPU's and memory of the era of your motherboard.
 
Although you say you bought the 8400GS video card last year, it is suspect.  I would start by reseating the video card (with the PC powered off, remove the video card then reinstall on the motherboard). 
 
This description from NVIDA on the 8400GS suggests it is an "old" video card that has been around since the Vista days so it too may suffer from Win 10 compatibility.
"Q: Who are GeForce 8400 GS graphics cards for?
A: GeForce 8400 GS graphics cards are ideal for cost-conscious users who don’t want to sacrifice features. NVIDIA GeForce 8400 graphics processors are great for watching HD DVD and Blu-ray movies on a PC, accelerating the Microsoft Windows Vista experience, and playing Microsoft DirectX 9 and DirectX 10 games."

You could always try another graphics card like this for $42.99. 
 
I tried one recently in my Win 10 rig to rule out what I thought was a possible glitch in my integrated Intel HD video.  That wasn't the problem, so I returned it.  Make sure the store where you buy from has a liberal return policy.  I just ended up paying return shipping, so not a big issue.
 
This is a low profile, fanless, nVidia GeForce GT 700 series. It supports DX12 and will run on Windows 10.  It is intended for home theater and integrated video replacement, rather than gaming, and it supports HDMI.
 
MSI GeForce GT 710 DirectX 12 GT 710 2GD3H LP 2GB 64-Bit DDR3 PCI Express 2.0 x16 HDCP Ready Low Profile Video Card
https://www.newegg.com/Product/Product.aspx?Item=9SIA1N83WZ4129

abacab, I like your Avatar.  Looks like the control panel on the 360-65 we had where I worked.
 

fireberd
abacab, I like your Avatar.  Looks like the control panel on the 360-65 we had where I worked.
 

I worked with some 360 era, and earlier, mainframes from other companies, but the 370 series was actually the first IBM that I worked with.  So I do recall when memory was measured in k, rather than megs or gigs, LOL!!!