My LS-Q2.0TL/R5 is exhibiting the same behavior. It will shut down randomly, and many times won't power on. Right now the green LED on the power brick is blinking, as is the ethernet link LED on the back. The date code on the Seagate drives is 11142, so roughly May 2011. Roughly 4 years of service or so, is that the best I can expect from a NAS? It has always been connected to an APC UPS750 pure sine wave UPS, and properly shut down during power outages before the UPS batteries ran out.
It is configured with 4x 500MB drives, setup in RAID10. It is running at near 95% capacity used too.
I can't get the unit to stay operational for more than 20 minutes at a time. I've copied over the majority of the files to a WD Passport Ultra, so I'm less concerned with lost data at this point. Using a USB to SATA adapter, I've pulled all 4 drives and run Passmark's Diskcheckup V3.3 on all 4 drives. All show "OK", although drive 4 did drop off briefly during one test, so I'm wondering if that drive is suspect.
As I need more capacity, I'm wondering if I should invest in new drives and see if that fixes the issue, or just punt on the 1 yard line here and go with a QNAP or Synology instead. Since I'm well beyond any warranty period, Buffalo tech support has been pretty much non-existent, so I'm left to troubleshooting on my own.