Multiple problems on a 4*280x rig

[TheUniporn]

I managed to install the drivers with all 4 GPUs on and now I'm not getting the "LoadLibrary failed with error 998: Invalid access to memory location." error anymore. The same GPU still has problems and there is a driver crash when folding starts. I'm going to reinstall F@H in about 3 hours after 2WU finish and delete the data but I don't expect much.
So far the CPU-RAM-MB seem rock-solid as before folding I never had any problems with it and it ran all the time for 6 months (with less than an hour per week downtime)...the only new component is the CPU (not sure what to do here except a stress test), which coincided with the start of this problem. But before that I mess with the CPU (not sure how), I will change the powered riser that I use and the place in the MB of the GPU just before the F@H reinstall.
Thank you all for your help!

[bollix47]

Were you able to identify why the drivers are now able to install with all four GPUs in the computer? Knowing that may be helpful to others.

Also, if you're going to move one of your GPUs to a different slot you might want to reinstall the drivers again before reinstalling F@H. Just to make sure the o/s knows where everything is and that the folding@home installer picks up the correct information. I know that may seem like overkill but it should eliminate any possibility of failure.

[TheUniporn]

I didn't use AMD cleanup utility before installing the new drivers, never had that problem in my life...until now. You might be right with not changing the GPU order just yet, I'll wait a bit.

[TheUniporn]

Final(?) update:
After installing F@H with all 4 GPUs present it seemed like everything was fine but I was still getting display driver crashes and one GPU not doing any work. Web Control shows after 12h+ that it's stuck at 99.99% and while running it was showing decent PPD but again, it wasn't doing anything. I found the problem for the crashes, it was because it was undervolted, I had the undervolted BIOS in the same place for all Gigabyte cards except for this one, everything makes sense now, it shouldn't have taken me this long, this is very embarrassing. Now in the log it shows the GPU is doing actual work starting from 1% (even if it's shown to be stuck at 99.99% in web control and work queue) as well as with GPU-Z.
Thank you everybody and I'm super sorry to have bother you with this.

[7im]

The webcontrol and fahcontrol showing 99% or 0% is merely a cosmetic representation that those programs don't have enough data to show a more accurate value. 99% is also shown when the GPU slot is starting, stopping, or crashed.

If you see 99% a lot, you need to figure out why your GPU is crashing.