Hi guys. I need help!

I've recently (within the last week) started encountering some quite serious, prohibitive issues when recording in Logic Pro 7 and hope that someone might be able to help.

NB* I'm not a Logic or Mac n00b, so be as detailed as you like/can!

Started a new track; using various EXS24, Ultrabeat, and also Reaktor 5 for a synth & an effects box. I know that my machine ain't 'all that' anymore so I make good use of the 'Freeze Track' when I'm not editing an AU part (it helps!).

The Problem -

I'm trying to record a guitar through my MAudio MobilePre USB, and am encountering problems. My live input strip has a bunch of plugins on it, most of them turned off; I'm only using Guitar Amp Pro on this occasion. When trying to record, and the track is running, it'll get to a point where a big guitar line (1 track, mono) comes in and then jitter & stop, telling me that the disk is too slow or the system has overloaded.

I've never really encountered this before. I try not to run anything else (I even have the AirPort turned off) while using Logic Pro as I know it's quite system hungry. This has only happened quite recently, and I'm concerned that either A) my USB device is buggered or B) my Mac has gone a bit doolally! I've reinstalled the drivers for the USB device, and am running it on the native port (not a hub; the Logic dongle, my mouse, and a MIDI KB are on the unpowered hub).

Does anyone have a suggestion as to how I might be able to fix this issue, as I've got a ton of ideas that I need to get recorded!

THANKYOU!