The reports from the international portals are a little too brief and are only partially correct.
Here's what's going on, in a nutshell
Brief Background
Gloria Macapagal Arroyo (GMA) came into power in 2001-2002 through a show of civil disobedience (commonly referred to as People Power II ) that forced then-president Ejercito Estrada (ERAP) to vacate his post at the Palace. Especially as the Army and Police both refused to support him and disperse the rallyists.
The protest was due to a move by ERAP's allies to block legal proceedings regarding an impeachment case against him.
Through political collusion between the Supreme Court and the political LAKAS coalition, GMA was sworn in as acting President, as she was VP at the time, and a LAKAS party member.
The Opposition party, which supported ERAP, staged their own "People Power" using paid-off demonstrators, but it failed miserably.
In 2004 (not sure of year), certain Army and Marine officers staged a "withdrawal of support" and show of force by holing themselves up in a hotel with arms, ammo and in full battle gear. They decried corruption in the military. They eventually stood down. Most of the leaders were arrested, the rest of the participants received demotions and suspensions.
GMA won the presidential election in 2004, but there were allegations last year that she cheated in that election using government funds (as she was president at the time). A voice recording, which many agree is authentic, surfaced that had GMA talking to an electoral official about vote-rigging. Word is that she used military officers to carry the money for the payoffs.
On the basis of this evidence, impeachment proceedings were about to be filed against her, but in a legal maneuver that was pure genius, GMA filed a case
against herself. The case was so weak, it couldn't be prosecuted. And as, under law, you can only be impeached once a year, she was safe.
Current Sitch:
This last week was the anniversary of "People Power". A lot of public protest rallies were scheduled for this anniversary, and permits had been issued already.
Late Friday, according to GMA's administration, there was a failed coup d'etat attempt, so she declared a State of Emergency. This nominally has no legal implications, as only Martial Law grants the President extraordinary powers. But she exercised powers close to those granted by Martial Law, by authorizing warrantless detainment and search and seizure operations. Initially, the government tried to rescind all rally permits, until legal eagles pointed out they didn't have the power to repeal them, as there was no Martial Law (hence, no rescinding of civil rights, right to assemble).
GMA went on air claiming that elements of the left, right and opposition were aiding the "coup attempt" against her.
During this State of Emergency, GMA had Crispin Beltran arrested for a crime supposedly committed 21 years ago (when the Philippines was under the Marcos Regime), she tried to arrest various leftists, and had some of them detained. She had a leftist newspaper searched and raided. She had a general detained. All without warrants. Some detainees were released as fiscals had nothing to charge them with.
As Beltran is a Congressional Representative, this didn't sit well with Congress. They're convening in a few days to discuss this.
In the meantime, General Miranda, Marine Commandant, resigned his post (according to the Government). His subordinates went berserk, claiming he was removed. 400 marines went to Marine HQ in a show of support. They had a standoff with General Miranda's replacement for almost twelve hours, as he negotiated with them. These Marines were talking of withdrawing support from the Government, and were asking why their superior was sacked without due process. Words shouted at the cameras included "We don't want cheaters (in reference to the President)", "Marines don't shoot Marines! (in reference to the word that the Army was going to attack them)", "we're withdrawing support (from the Government)", "We're here to hold a prayer vigil (for General Miranda)".
These are badass Marines, mind you, in full battle gear, and with APC and tanks.
General Miranda has not released any public statement. It is said that he had convinced the Marines
not to withdraw support from the Government last week, but that he resigned for personal reasons. But then, it is possible he was allowed the opportunity to resign instead of being sacked (as that always looks better on your resume.

)... if he indeed averted a public secession of the Marines previously, it is unknown why the Administration would sack him.
International media outlets say both Miranda and Col. Querubin, the group leader, were sacked for the coup d'etat... this isn't true. This isn't the Government line, and this isn't the Marine protesters line. I have no idea where this came from. The averted coup attempt was supposedly by the Magdalo group (the group that seceded at Oakwood).
What is true is that Querubin asked for public support, and he got politicians from the opposition descending upon the camp. Must have been distasteful for him...
During the standoff, the Government has repeatedly asked media outlets
not to cover the event, as it was an internal matter of the military. Platoons of soldiers were staged
outside media outlets in preparation for hostilities. The Army was asking media not to report on their movements (that much is understandable) and opposition groups, various leftists and religious groups were gathering in preparation for mass civil disobedience (strange, as this was an action originally by rightists...

) and the city was entering a lockdown phase (checkpoints on all major arteries) despite reassurance from the Government that no troops outside the metro were defecting or moving around.
The standoff ended, though, and the chain of command of the Marines has been reestablished. The protesters are left with nothing to protest, (and these protest groups are laughably small, anyway, mind you... the rest of us are sick and tired of rallying) and we're all left scratching our heads, going WTF?