Disconnecting the PC from the Internet (in and of itself) won't solve anything.
Where you get into issues:
- Deeply entrenched A/V software (can cause performance related issues as well as trouble with authorization, etc)
- Sending/Receiving Email (your greatest risk of infection/malware)
- Automatic Updates (an update could potentially adversely affect performance)
- WiFi is notorious for causing higher DPC Latency (some adapters behave much better than others)
Here's what I'd recommend:
- Reload the machine so it's as clean/lean as possible.
- Tweak the BIOS/OS so that DPC Latency is as low as possible
- Disable power-management type features
- Disable scheduling services and other intensive operations that shouldn't be constantly running in the background.
- Disable Automatic Updates (manually check/install - make sure you have a backup prior)
- Don't send/receive Email on the DAW
- Make sure you have an up-to-date backup image file (using True Image or similar)
In short, you want a clean/lean machine... that's built/tweaked to sustain heavy loads (without hiccups in data flow). Do these things... and you'll have a trouble-free DAW.
Although rare, in some cases you may need to swap out hardware to achieve maximum performance.
FWIW, I've got my DAW connected 24/7 (no A/V software)... and it's never been infected.
A little common sense really goes a long way...
With the backup image file... even if the worst happens... you can reload and be up-and-running in short order.