Hey all, could use some advice on some troubleshooting if anyone has suggestions. I have a previously bulletproof 2010 Mac Pro running 10.11.4. It's been modified a bit: -Hex core CPU upgrade -The usual RAM upgrades -Boot drive is Sandisk Extreme Pro on PCI card (Velocity Solo X2) -Inateck 4 port USB3 PCIE card -EVGA GF 680 card, flashed to Mac BIOS (same physical card as their Mac version) -802.11AC Wi-Fi and Bluetooth 4.0 upgrades (from MacVidCards) -Internal Blu-ray and HD-DVD drive in second optical bay All of these upgrades have been in place for years with no issues. Suddenly the system will beachball and hang there, with a hard power cycle as the only recourse. Sometimes it remains stable for hours, sometimes minutes. This behavior started on Friday and it's seemingly random. There isn't any consistent pattern regarding usage that triggers this. Sometimes after the beachball begins, an app or two will close on its own as things hang. I tracked down my old install disks and ran AHT over the weekend. It passes normal and advanced tests with flying colors. Temps look fine, fans are working normally. There isn't anything suspicious in the console logs. Any thoughts? I'm fine with throwing a few dollars into a repair since it's my work machine and I don't see anything on the horizon that I'd want to replace it with. I just don't know where to start. Edit: Extra symptom that might or might not be related. For several months, there would be occasions where the system wouldn't recognize USB devices that were newly plugged in. I'd have to plug/un-plug them a couple times on occasion and then it would be fine.