So i have a presonus usb audio interface , I have my mic in one port and my guitar in another , On the back i have a connection for headphones .
I want to be able to play my guitar through a random plugin and hear it back real time .
 
But i plugged in my headphones earlier and changed the output on the track to my Audio devcice and the audio is slow and not sounding right .
 
I have a pair of Astro A40`s and wanted to use them purely for hearing my guitar in real time .
 
Am i not changing the right settings somewhere or something  ?
 
 

Hi. It sounds like you have latency issues. Do you use ASIO drivers with your Presonus? If not, i would recommend downloading it and install it. Then try lowering your ASIO buffer in Preferences (P), Audio, Driver Settings.
To check if anything else is giving you latency issues, try this: http://www.thesycon.de/deu/latency_check.shtml
Best of luck.

Thanks for the reply , I appreciate it 

It's called round trip latency ( RTL)  and is the result of all the processing your signal has to pass through to get from your guitar back to the interface. 
To get there it has to run through a gauntlet of processes that each add latency.  Your A/D then the USB then the DAW, your computers processor,  interface drivers, then back through the USB and lastly the D/A. Audio drivers and your computer are the weak link and it is there you look for latency. Not all interfaces and systems are capable of low settings to eliminate this. Low RTL can cost money. Budget interfaces often use hidden buffers and there's no hope of real low RTL. interfaces made by RME and MOTU and then some of the firewires are know as good performers. 
The solution is to lower your settings but this often causes instability and dropouts. My guess is your interface will not do much better than 7ms of delay which might not bother you. For my system to be rock solid stable I need to keep my setting at 256 and this results in RTL of 12 or more as example. That's my Focusrite, My TAscam can do no better than 25ms. This doesn't bother me as I don't use guitar sims. I can muck about in stand alone, but forget it on a projects. 
 
Most interfaces have direct monitoring which eliminates RTL by allowing you to monitor your input directly. Some have a mix or blend control so you can then mix in what is coming back from your DAW.  

One thing I've taken to doing is to run my sims in standalone mode while playing/recording in Sonar. Guitar Rig is especially good for this since it has very little latency. When I'm happy with the take I then pop over to Sonar and fiddle with the sims in the box. This process is certainly a less than perfect solution but it will have to do until I can justify a blazing RME PCI interface for my goofy little hobby.

My solution is a good old fashion formula.
Good guitar with good pups
Good tube amp
Some stomp boxes.
And I now am sold on my Blackstar amp too. It can be shut off in the room if I go direct. But I am a miked speaker person from way back.
In other words, I can easily get a great tone before I hit the record button, and important to me I can also play that live.
To me the sims are great for guitar players who are still experimenting with weird effects and tones and don't want to spend the money on the hardware. For me it has to be the hardware first.
I'm not against sims at all and I do sometimes add reverb, delay or a chorus to a recorded track via the effects bin. But they just don't cut it for me for using in real time. I'd need a much better CPU and interface. That's $500-$1,000 wasted for me. I'd rather spend that on hardware guitar tone.