My Sony Ericcson K850i has stopped working. It is sort of alive- the alarm went off this morning at the right time. I couldn't turn it off though. I cannot turn it on, call people, access data anything it is meant to do. I am unable to update the software, nor can I repair it via the SE website. The three most recent attempts have caused my PC to crash. Any suggestions?

Put your sim card in another phone….use that til you can upgrade to a new phone 😀

Seriously though – is it pay-as-you-go or contract and how old? you could get it repaired if it is in warranty (SE give you 12 months) or if you have insurance get a replacement.
OR
Try it without the memory card in – most of the time memory cards affect a phones performance even with little stored on it.
OR
Try a master re-set (see user guide) back up any data to your memory card first if you can and take out your memory card before the re-set.
Otherwise my first response is best 😉

looks like it might be suggestion 1 then 🙁