High Load warning from web hosting. HELP!

My site runs Zen Cart 1.3.7 and works well aroung 1 year, but this morning i got a warning email from webhosting, they said my have high load issue and if dont fix they will suspend my site. Can anyone help me for this issue?

Here's the mail i got from webhosting:

System administration has been tracking high resource usage on the machine housing your account, and has traced it to your site, dz-tech.com.

The files showing high load are as follows
index.php?main_pageindex
index.php?main_pagelogin

At this point, due to the repeated warnings, you must correct this activity immediately. If you do not contact us, we may be forced to suspend your site.

Please let us know your plans in this regard as soon as possible to avoid any downtime in case this problem cannot be resolved.

My Site URL: www.dz-tech.com

You might consider getting a real hosting site for managing php, MySQL and e-commerce ...

The Hosting link at the top of the screen has a list of our Certified Hosting sites that are aware of how to configure servers for businesses such as yours ...

Unless you have a logic error on both those pages causing looping (which seems unlikely) then you are either attracting lots of traffic (a good thing, not something to be fixed) or you have been the victim of an automated attack (which is likely to pass since Zen Cart is fairly well protected from these attacks so they'll move onto somebody using a more exposed cart).

Either way, your host's response isn't very helpful. I'd recommend that you ask for me details about the nature and timing of the high server loads and if they aren't a bit more helpful than they've been to date, take Ajeh's advice and replace them with a better host.