Am having two strange problems that are starting to eerk me with this (relatively new) computer, running Debian wheezy:

1. If I boot anything later then 3.12 kernel, I don't get any display. As in the monitors display black. No cursors of any sort. Changing to a virtual console doesn't help. Booting in rescue mode doesn't help (I think this rules out X-Windows being a problem). If I go back to the 3.12 kernel, everything works perfectly. I also tried plugging monitors into alternative ports just in case it is going to the wrong place, but get nothing - in any case, under 3.12 the computer seems pretty good at automatically working out what ports are active under X-Windows.

Am currently using the non-free nvidia drivers. Had exactly the same symptoms when I installed the latest kernel without the non-free nvidia kernel modules. I think the problem is occurring before X starts.

Computer seems to be up and running, and responsive to crl+alt+del despite not having a display.

2. There seems to be some weird performance problem. e.g. save a 2 kilobyte file in vim, and the computer can completely freeze (all other windows, including xterms, stop responding to user input) for, say 30 seconds, while it is writing that file. Chromium takes ages to load with several tabs, and pages can fail to start properly while it is doing so.

Computer has 16GB RAM and is not using any swap. It has 11GB of buffer/cache space:

Problems occurred before starting chromium, previously I wondered if it was chromium's fault.

This is moving disk + RAID1 + LVM + ext4. Bonnie++ results seem to be pretty good, better in fact then my work computer, which doesn't suffer from similar problems.