Have a strange behaviour in one of my zen cart shops.

Suddenly, about two days ago, it became so slow, both admin and catalog pages.
Weird enough, cause my other shop (they're on same server) is very fast.

Fast shop: www.lineagotica.it
3800 products
Parse Time: 0.617 - Number of Queries: 328 - Query Time: 0.159171928192

Slow shop: shop.corimtec.com
650 products
Parse Time: 0.262 - Number of Queries: 238 - Query Time: 0.0749762357178

I tried to optimize slow shop's tables without results (looking to parse time, it seems not a DB issue)

Can you please help me to debug this problem?

Francesco