Arduino Mega 2560 two interrupt issue

1. I am using arduino mega 2560. Connected are 20 segments together, refreshed every 500us. After every 500us, one segment is enable & written.

2. Also a PS2 keyboard is connected to read keys & display on segment. Library used is PS2Keyboard.cpp - PS2Keyboard library Written by Christian Weichel<Snip>.

3. Ps2 & timer refreshing code of 20 segments works independently correctly. Problem arises when I merge both codes together. In that case what happens is I am not able to read correctly...

Arduino Mega 2560 two interrupt issue