@StreamFinder -- I'm not a doctor, but from what I understand, there are a few different types of platelet function disorders.
They can fail to adhere to one another, for instance, in the case of Bernard-Soulier Syndrome, or they can fail to secrete properly.
This is called Gray Platelet Syndrome, and usually shows up as a long bleeding time, and a low platelet count.
Among other things, platelet disorders can be acquired as side effects of medication, or because of certain diseases.
In fact, some antibiotics can cause the platelets to malfunction, as can antidepressants and some blood thinners.
Finally, kidney disease and leukemia can be cause platelet disorders.