MySQL huge CPU usage

[Asdrúbal Suárez]

Hello everyone, I'm using MySQL 5.1 in a VPS (I'm aware this is an old version but at this moment updating it is out of question). We're having troubles on this server because the CPU usage is extremely high (Around 100%). I checked the status of the Qcache variables giving me these results:

Qcache_free_blocks 576
Qcache_free_memory 265752168
Qcache_hits 3043015
Qcache_inserts 83302
Qcache_lowmem_prunes 0
Qcache_not_cached 1426561
Qcache_queries_in_cache 1564
Qcache_total_blocks 3759

I believe from what I'm seeing that there are many queries which are not being cached by the server. Still I don't know if this is the main cause of this huge CPU consumption. I will give more information as soon as possible. For now, what should I check? Do you think my suspicions could be right?

Thanks in advance