disk at 100%, windows so slow

[Hey Adrian]

http://prntscr.com/jn7wd2
heres a screenshot of when i first start up windows. any help please?

 

[SkyNetRising]

Use Resource Monitor (Disk Tab) to determine, what's causing this.
Locate Disk Activity section, order it by column total and you'll see processes causing the activity on top (and also files being used).
Post screenshot.

 

[CaptainCretin]

Those read/write speeds are terrible, do you have any SMART warnings??

Other possible causes include

Windows Search (indexing the drive - can be turned off).

Malware (I would expect to see high cpu activity if it was this).

Two programs conflicting each other on start up. You can sort this by stopping one from starting at boot up to see if it sorts the problem, and there are ways of setting a delay before it tries to start if needed.