Had a couple of songs that had been developed with AD drums while waiting for a drummer to have some free time.  Yesterday I recored the drummer with real drums (8 tracks)....packed up for the night. 
Starting to mix today I noticed there is a lag starting and stopping the tunes of about 1.5 seconds.  There is also alot of cracking, popping and distorting going on.  Nerver before had this problem.
 
I found that if I deleted all plugins the clicking, popping went away but the lag is still there.
 
Any thoughts on the cause??
 
Thanks In Advance....

http://www.sweetwater.com/sweetcare/articles/pc-optimization-guide-for-windows-7/
 
Hello Meh, I saw this link from one of our friends and I think you can try it. Best case is that the recording was good and playback /mixing can be improved with something like this. Worst case is that the recording is also affected. Anyway I hope it helps you. 
 
 

Did you happen to add effects to the project recently?  Some effects are meant for mixing/mastering, and not for real-time use while tracking.  Some of these either use a whole bunch of CPU and/or use look-ahead processing, and can introduce instant latency.
 
You could try loading the project, then hitting the 'E' key on your computer keyboard, which toggles off/on the bypassing of all effects.  If you pops/crackles/dropouts go away after bypassing effects, then you know that one or more of these are contributing to latency problems, and you can begin evaluating these to determine which are causing this.
 
(hitting 'E' again will toggle effects back on, so you can do all of this just for testing purposes, without hurting anything)
 
Bob Bone
 

Sample Rate can impact your ability to handle lots of tracks with lots of FX.
Recording your tracks at 192 makes more work for your computer when applying FX compared to 44.1.
 
Sometimes lag and performance problems like this can be caused by Virus Scanners. Wave files are usually only scanned once, but scanning large files can use a lot of Disk IO and get in the way of your playback. Scanning usually starts the second you hit stop on your recording and files are committed to the file system. When this is the case, the problem should fade away if you leave your computer on for a while where you are not recording.

+1 for the above.
Most likely a plugin issue, virus scanner a common cause as well.
Plus run chkdsk, defrag and disable intel speedstep in BIOS assuming your CPU is spiking.
 
Does the issue happen for new projects?
 

Maybe you playback buffer is set to high? Set it to 64 or 128 and see what happens. If that doesn't help, then it may be something else in that particular project causing it that you over overseeing or your sound card ASIO drivers are set too high
 
CJ

What are your Playback/Record I/O Buffer Size set to?