Port no longer recognised

I re-set the USB ports on my Dell as they were causing issues within another program. Now my MATLAB code no longer recognises my device (see below). What do I do to resolve this? Thanks.

***** PST Box is ENABLED *****

***** USE Key 1 for PVT *****

******************************

Error using serial/fopen (line 72)

Open failed: Port: COM3 is not available. Available ports: COM5.

Use INSTRFIND to determine if other instrument objects are connected to the requested device.

Error in Control_PSTBox_Select (line 120)

fopen(objPSTPort);

Error in Run_KSS_KDT_PVT (line 130)

Control_PSTBox_Select('OPEN');