Problem with HD 7770 in Windows 7

On GPU Tweak, the temperature shows just around 30-35 C. I think when I was gaming it was in the 60s. I didn't check just before it had the problem, but I don't think it was pushing much beyond 70, if it even got that high.

I tried reseating the card and the power connector, but still it gives me the same problem. I even tried it in the other slot on my motherboard, but same issue.
I tried reinstalling the drivers that came with the CD, and they reinstalled fine, computer restarted fine, but then I have the same problem when I open up most programmes. Most Microsoft Office programmes work fine, but VLC, Windows Media Center, etc. immediately give me the pink screen.
When I booted in Safe Mode, I was able to open VLC without issue. It might have had some warning about not displaying properly or something.

By the way, in the first post I said that my Motherboard EZ debug light for the GPU shines red. It does so for roughly three to four seconds just before the MSI screen comes up.

Okay. Thanks for your answers anyway.
Still, I find it strange that it seems to work perfectly fine in Safe Mode, but I guess its not under stress.
Somebody bought the GPU for me around four years ago. Though I haven't used it for almost a year as I had problems with my motherboard and CPU and just replaced them two months ago.
Do you think I should try a fresh Windows install, just to see?
Oh, and if I test the GPU in another PC, do you think there's a risk of me spoiling something in the other PC? I could try it in a work one, but I can't afford to cause problems on that computer.

Weirdly, last night I updated my antivirus, and then I was able to open the programmes I couldn't open before with no problem. Not sure if it's a result of updating Kaspersky or something else, but strange all the same. Still, the GPU EZ debug light on the monitor shines. Also noticed that the CPU one shines as soon as I press the power button, but not sure if that's normal or not.

Update 12/08/2018:
Okay, since this post I was able to run my computer normally without issues. Yesterday, I even did some recording and other fairly light work in Sonar and Vegas without issue. I installed GPU-Z to monitor my graphics card and realized that the processes and game (FIFA) I was running were not putting a lot of stress on the graphics card.
Seeing that the CPU was still giving a red light when I turned on the computer, I tried reseating the RAM and just leaving one stick in at a time. When I took out the stick from DIMMB2, though, the RAM light on the mobo turned on. I removed the stick from DIMMA2 and placed the one from DIMMB2 into there and there was no more light, but still the CPU and GPU ones. When the computer started, it went into the BIOS and said something along the lines of settings being changed or something like that. I just loaded the default settings and it started fine.
I restarted the computer a couple times to test stability, ran some tests, and it all showed up fine. Finally, I decided to try World of Tanks again to see if it would still give me issues. I dialed down the settings a little more and played a number of games while monitoring GPU-Z and Resource Monitor.
The highest temp the GPU got to was around 75 degrees. CPU didn't exceed 55 degrees. VRAM went to around 1.3 GB when under load. Generally, it seemed to be working fine, though...and then it gave me the pink-coloured screen. I turned off with the power button, waited for a few minutes, and then tried to restart...Mobo lights up, fans spin, CPU debug light shines...and then nothing. It doesn't even enter the BIOS, something it never failed to do before.
I reseated the GPU and RAM, but still the same thing. I tried my old GPU (that doesn't really work, but at least used to display picture with all sorts of coloured artifacts), but still nothing at all.
What do you think I should do?
If I take the CPU cooler off to check the CPU, do I need to apply new thermal paste? This is somewhat worrying.