Long shot but ... I have an  that was installed on a  (socket 1150 w/4670k). I had a server with an AMD FX-6300 +  and a Hyper 212 Evo. I moved the 212 over to the 4670k and then tested and no video from the GTX 970. Onboard video on the H81L works, and an old GeForce 8400 works in the PCIe slot. So I know the motherboard is ok, I also tried different RAM and PSU with the mobo + 970 since I have those. Tried the 970 on the AMD mobo with same RAM and PSU and it works. I tried switching the BIOS on the 970 (has a switch on back to switch between 2 diff BIOS, I've never flashed it so they would both be stock). The 970 works on the Gigabyte mobo with the AMD proc. Both mobos appear to be Gen2 PCIe. Thinking it was the motherboard I ordered an eGPU (Akito Node Thunderbolt3) and tried the 970 in that and it won't work either, the 8400gs did. So after all that there appears to be something weird with the GTX 970, really weird. This is my casual gaming dad rig and I'd love to get it working with the 4670k again because it's a much better gaming proc.
970 + 4670k + MSI H81L = no work
970 + 6300 + Gigabyte GA-78LMT-USB3 = work
I cannot find any physical damage, no accidental nicks or scratches. Both 6 pin power plugged in. Tried reseating. Tried outside of case and in (no standoff issues). I don't think it's the motherboard since the eGPU didn't work either. Reset BIOS on both motherboards as well. 
tl;dr - It's a long shot, but maybe someone has an idea. My GTX 970 stopped working on anything by an old Gigabyte GA-78LMT-USB3 motherboard ... why?

now that kinda sounds like a bios compatibility thing  .  when the 900 series came out quite a few boards needed a new bios to add support of the cards    on the board be sure you got its latest bios 
I see the latest one for the MSI H81L offers support for   Improved AMD Graphic card compatibility. and a '' Updated VBIOS and GOP Driver''   [what v bios is for a motherboard ?? I thought a vbios was the vid card's bios  maybe for why your egpu you said was not working as well ? ]  , but nothing said for NVidia  .    evga cards were hit by this a lot  and guy with out a bios up date to help RMA'ed the evga card for say a MSI card that did work when the evga did not .     . evga had the 2 - 970's that were kinda oddball  like will not sli with another evga 970    .
 
maybe just a evga 970 you got has a hard time with the bios's handshakes
 
 https://us.msi.com/Motherboard/support/H81I

ya ,  if you look at like older z68   was one hit hard  and needed a bios update and like a dell xps 8700  needed it as well   for examples .  
 
one thing I do recall was guys with evga cards  not working but replaced them with a msi 970 for example worked right out of the box  ??  
 
like my board  I was worried cause its a asrock z87 extreme 6   and did not get a bios update  for cards but its little sister  the z87 extreme 4  got some  for gpu compatibility  , but the 900 cards did work in the 6 fine anyway    so I got to wonder why the extreme 4 needed new and late bios but the extreme 6 did not ? 
 
seem like all ways somethings up with the 900 cards  and then treated like the unwanted redheaded stepchild  series ...lol...    once you get it working then hope it don't ''burn up'' on you ...lol...
 
''Maybe I just nicked something somewhere on the GPU''   maybe the egpu [I guess that's the onboard /cpu vga]   may not be working ?
 
intel can get bent pins if not carefull  . that's a possibility. may need to check if necessary.    
 
 

What BIOS version does your 970FTW have?  

this so far been the closest issue I found [ asus 970]
 
https://steamcommunity.com/discussions/forum/11/527273452871454587/
 
don't know , maybe one of them boards thst you got to get super lucky to get the right gtx970 to work in it or if at all  ..   even back before some just were left S.O.L    and go with another non 970 card or a new build/motherboard that would take one ?
 
ya got to kinda think the 970 card is working fine in other builds  and other cards seem to work fine in that MSI board ?  maybe just hard luck  on that   combo
 
 
too bad not telling what 970 he was using ?
 
Great So Far
Other Thoughts:            Used this on a build with an i7 4790k & GTX 970 in a dual boot setup w/ Win 7 & OSX Yosemite, and so far it's been very solid
https://www.newegg.com/Product/Product.aspx?Item=N82E16813130735
 
did not see anything in like amazon reviews of that card issue ?
 
like said could be just something with a certain  model of evga or asus 970's like above just not being compatible ?    maybe if you had a MSI gtx 970 to see how it goes in it ? 

mindaugas

Chopper3200
What BIOS version does your 970FTW have?  

According to EVGA XOC - 84.04.28.01.71

Bios version 84.04.36.00.71 is available for the 970FTW.  But I would look closely at the back of the card, see if you scraped a trace or a missing capacitor coming from the pcie slot connectors area.

if it worked before you swapped the heat sink on the card check to see if on that msi board that the pci-e slot blade of the card is able to go all the way down even and correctly in to the boards pci-e slot
 
one guy put a cooler on a card and the board he was using it [back end of the card ] would then rest on  the sata ports of the board just enough to keep it going in all the way and not work ??  make sure with a itx the memory slot clip / latches are not doing the same    most need to be in the locked / up position  for clearance of the card .
 
 
like you say it works on the other mobo fine , so ??