Maximum possible memory usage: 16.2G (874% of installed RAM)
Staring at the mysqltuner output, I see something disturbing
[--] Total buffers: 1.7G global + 18.6M per thread (800 max threads)


The 800 is the max_connections.
The 18M is a sum that includes read_buffer_size + sort_buffer_size + join_buffer_size

What is 800 * 18M ?
mysql&gt; select 18 * 1024 * 1024 * 800 / power(1024,3);
+----------------------------------------+
| 18 * 1024 * 1024 * 800 / power(1024,3) |
+----------------------------------------+
|                                14.0625 |
+----------------------------------------+
1 row in set (0.00 sec)

That's 14G your DB Server cannot handle.
RECOMMENDATION
Add this to my.cnf
[mysqld]
sort_buffer_size = 1M
join_buffer_size = 1M
read_buffer_size = 1M
max_connections = 100

then restart mysql and run mysqltuner.pl again. You will see lower numbers.
Give it a Try !!!