High Interrupts and DPC in Windows after reboot

We have seen this several times in Win 2003 R2 32bit, XenApp 4.5 server where we have to reboot them to get rid of the problem. Sometimes more than once. We've had this issue on both smaller virtual servers and physical servers.

This is what the Interrupt and DPC graph looks like in procexp

(Scale is to 100% of total CPU)

Obviously it is impossible to work with interrupts this high. The server barely responds.

Any idea as to what this is?

Only theory I have is that it is tied to a too high user count, since it has almost disappeared after we lowered user count on many servers. And possibly exhausted non-paged pool (32 bit).