|Check free disk space:|
df –h # general info
du –hs /* #specific folders
If there is no room, delete unnecessary files.
A common situation is when the logs are growing and disk space is not available, MySQL can not work properly (true for all other services - apache, exim, etc.)
restart MySQL again:
If the cause of your problem is not shortage of a free space, then in the log should appear an error depending of the problem. Errors can be various. What happens next depends on the specific error and require detailed investigation. So, check it and write about the result.
Also here might be something interesting, perhaps