You are going to need to rebuild the card if you want anymore use out of it. After cleaning the cooler out you must replace the failed inductors that have shorted out. The rest of the card should have little or no problem but when the screen goes pink or shows blocks usually the gpu isn't getting enough power even at reduced clocks to even display an image correctly. I own two and had a third gtx280.
The safe range is R45 through to R60, the original inductors were not meant to last and you got a long time out of your card as is. Replace with R50 inductors from any mainboard or buy in bulk lets say a pack of 20 from any online store that sells them. Once you have done that the vrm phases will work like they used to and power will be restored. The card will actually will hit higher clocks with the mod.