JFrame displays without its components or settings (please help)

Question

On clicking a button in an app, due to computational time required, I need to have a message popup that says 'Please Wait', which vanishes on end of needed computation. For this, I have a small working class MsgDiag that simply displays a non-modal titled JFrame showing a message string in a JLabel and an 'ok' in a JButton. This works fine when invoked directly via its own main method as a standalone, but when called from that other application(also a extended JFrame) via button click, it just brings up a blank grey untitled JFrame without the components (JLabel and JButton) or the background color! It does stay up for the required duration and vanishes on disposing its JFrame as expected but why blank w/o components or settings ?
I also find that though the JFrame component comes up blank grey, if during the computation portion in calling application, if any info/errors are popped up via direct call to a JOptionPane().showMessageDialog(JFrame(),msgString, titleString, msgType), then along with that modal popup (from JOptionPane), the grey JFrame gets correctly drawn with components and background !
Does this provide any hints ? Since MsgDiag works ok by itself I am puzzled.
I also tried putting basic code from MsgDiag (creating JFrame, adding its components, setting it visible etc) into the other app directly but same grey blank frame results. Had there been a non-modal JOptionPane I could have tried using it. I use JRE 1.4.2

Answer 1

Per your suggestion, I tried putting computational part in a different thread. Also tried putting the thread priority for computational thread to lowest.
In other approach, also tried putting the GUI popup (frame2) in a separate thread with highest priority while lowest priority computational thread executed. But neither approach worked. Still shows frame2 as blank w/o background or components inside while low priority computational thread finished, when frame2 gets disposed as instructed.
In 1st approach, also tried adding validate() following setSize() as some other posts have suggested but that did not change anything. Any other pointers ?