My site have been in trouble for several days..

sometime it says that:
"The page cannot be displayed
The page you are looking for is currently unavailable. The Web site might be experiencing technical difficulties, or you may need to adjust your browser settings.... "(not 404)


but at the sametime another XOOPS in the subfolder use the same database works fine. and the php checker in the root folder also works.

Today the host told me that my site makes the cpu usage up to 100%

I just have two hacks in my site one is show the rank images in the topposter block.
another is make the larger images auto fit the table.

Will these cost so many resource?

That sounds weird, normally image manipulation is cpu intensive, but not on small images, are you resizing large images to small ones on the fly all the time, this could hammer a machine. Try to keep the images in the right size and resolution, if that is not possible change the hack to do the manipulation once and then use a cached image.