Starts up - goes black - re-lights on shutdown - - Help Please

My Impression seems to go through the initial start-up, but quickly goes black and stays that way regardless of touching the screen or pressing the buttons or keyboard.  Upon shutting it down, the screen lights up and finishes shutting down.  Re-starting the phone just repeats the process.  Any ideas?

I shutdown by holding down the phone hang-up button.  Same as the startup.  It's the only button that seems to have a visible reaction on the screen.

After reading several Help topics, I got TKFE working and thought I'd try to backup the phone files.  While doing so, the phone lit back up and seemed to work fine - but only for a while.  Here are the symptoms:
1. The phone powers up and shuts down, but sometimes during the power up the 1st screen with the - what I'd call the loading progress bar - doesn't seem to go to the end.  Then the next screen with the colorful graphics pops up, and a second or two later, the screen goes black. 
2. Even though the screen remains black, when the phone is powered down, the screen lights up for the brief time while the phone powers off.
3. Yesterday and this morning, the phone sometimes acts normally, but then goes black for a while.  If I open and close the keypad, sometimes nothing happens and sometimes the phone lights back up.  The only thing predictable is the unpredictability?

Question:  Should I be looking at posts in a different Help topic or should I reflash the phone?  BTW, I'm not sure what reflash means or what, if anything I need to do first, like backup - so I'll start to read up on the forum.

Thanks

Thanks for the guidance.  Right now the phone seems to operate normally.  If it gets tempermental again, I'll follow your advice.

PS - I'm not very daring when it comes to computers or cell phones, but this forum and folks like yourself who freely share their time, creativity and experience have given me the confidence to try some things and make the phone more functional and fun.

Thanks again.