mysql freeze/crash on JOIN

Question

here is query:

SELECT nw.news_id, nw.title, nw.description, nw.url, nw.date, nw.image,
       nw.status, src.title as src_title, src.keyword as src_keyword,
       src.url as src_url, src.icon as src_icon, cat.title as cat_title
FROM news as nw
INNER JOIN sources as src ON nw.source=src.source_id
INNER JOIN categories as cat ON nw.category=cat.category_id
WHERE nw.status=1
ORDER BY nw.news_id DESC LIMIT 0,140;

news table size is around 30MB. server RAM is 1GB.

my.cnf:

[mysqld]
max_connections = 120
key_buffer = 32M
myisam_sort_buffer_size = 32M
join_buffer_size = 8M
read_buffer_size = 8M
sort_buffer_size = 32M
table_cache = 1024
thread_cache_size = 286
interactive_timeout = 25
wait_timeout = 1000
connect_timeout = 10
max_allowed_packet = 16M
max_connect_errors = 10
query_cache_limit = 8K
query_cache_size = 32K
query_cache_type = 1
tmp_table_size = 16M

[mysqld_safe]
open_files_limit = 8192

[mysqldump]
quick
max_allowed_packet = 16M

[myisamchk]
key_buffer = 64M
sort_buffer = 64M
read_buffer = 16M
write_buffer = 16M
local-infile=0

it was myisam I converted to innodb for better performance but nothing changed so I get back to myisam.

query works correctly on localhost but when ran in server, get high load and eat all RAM until crash mysql. just one of above query get me highload! something like that mysql could not finish it. table has around 50000 records.

I tried to fix issue by changing my.cnf parammeters with no luck.