On Wed, 04 Mar 2009 17:09:10 -0800, David Nebenzahl
wrote:

On 3/4/2009 4:46 AM Ken spake thus:

Brad wrote:

I have a Compaq Presario 1200XL laptop computer that one day, would
not power up. I tried another power supply, replaced a dead
RTC/cmos battery, etc. I removed the RTC battery, main battery, and
put it away. A month later, I decided to try it again. It powered
up! Everything seemed just fine, but it only lasted for a couple
days before it happened again. Again, I put it away. A month or so
later, it powered up and again everything seemed just fine. I
downloaded ROM Paq SP15611 and I "flashed" the bios. About a day
and 1/2 later, the laptop "died". Now it won't boot up. Again after
a long rest period, it came back to "life", but for how long? Note:
It won't power up after a week's "rest", but it will power up after
a longer rest such as a month!

If it were my computer the first thing I would do is clean the
contacts of the RAM. It sounds a lot like a bad connection and the
RAM is essential to it booting to even a bios screen for most
computers.

True, but it's hard to see how that would explain the bizarre behavior
the O.P. reported (what, do the memory chips magically unseat
themselves, then reseat themselves in the interval?).

Easy to explain: the notebook has a (large) capacitor that is across
the backup battery so that when that battery is replaced, the settings
are not lost. He removes the backup battery, then in the (couple of
weeks) time the capacitor finally discharges and the configuration
settings are lost, and the computer can reboot.

Many of these (not all!) have a jumper somewhere that will short that
capacitor to give the same effect.

Above reply does make assumptions as to what teh OP is doing, however.
g