Audio on some tracks stop playing out of nowhere

I am having a problem with Cubase when I have alot of channels in my project (40+) some of my tracks audio stop playing and come back in as they please.(The channels are not muted, and are not automated in any way which I find weird). Also Cubase Crashes often when alot of channels in my project and also takes a while to open vsts, the mixer, & the eq when I try to open it.

Computer: HP XW8600 Workstation
Processor: Intel® Xeon® Cpu e5430 @ 2.66ghz (2processors)
Installed Memory(Ram): (3.25 gb usable)
32 bit operating system

All help is appreciated