Some more info needed.
Is there another OS installed except PCLOS and Win7?
If not which was last installed ?
You can try this: go to LiveCD PCLOS session and try Menu-->More Applications-->Configuration-->Redo MBR (Restore MBR, LXDE Restore MBR). The last one depends on which version of PCLOS did you install (e.g. KDE, Gnome etc.)