Crusades

1067-1071.

Emperor during battle of Manzikert. Defeated and captured by Alp Arslan. Freed and had to provide: 1.5 million gold coins and 360,000 in annual tribute, Manzikert, Antioch, Edessa and Heiropolis, emperor's daughter as wife for his son. Killed when he returned to Constantinople after denouncing his claim to the throne to Micheal Ducas.

26th August 1071.
Military problems: Army had been depleted by previous emperors and Romanus relied on mercenaries (unloyal and can be bought), troops from different area had conflict with each other so didn't work well together, many troops heavily armed so slow compared to skilled, quick Turkish army.
Betrayal: Joseph Tarchotes (main general) fled with half of Romanus' men after they split, Andronicus Ducas (reguard from rival family) told mercenaries Romanus was dead during the battle so they fled, other Turkish mercenaries fled to Seljuk camp during the night.
Alp Arslan tactics: Romanus underestimated the skill of the Seljuk Turks who were much quicker and outsmarted the Byzantine army.

Economic: Inflation led to riots, cost of employing mercenaries to put down coups (trying to overthrow the emperor) and deal with Seljuk threats, gold nomisma lost a quarter of its value.
Military and Territorial: Seljuk tribes advanced to Anatolia. By 1077 Anatonia had been virtually overrun. In 1071, Normans under Robert Guiscard captured Bari ending five centuries of Byzantine rule. Byzantine empire didn't have enough soldiers to cope with the threats and had to hire mercenaries.
Political rivalries: coups came from within the ruling aristocracy. A Norman Roussel of Bailleur, betrayed the emperor and set up a self declared independent state in Anatolia. He proclaimed John Doukas emperor but was tamed by mercenaries sent by the emperor. Nikephorus Bryennius rebelled in November 1077, marched to Adrianople and was announced rival emperor. He was squashed by Botaneitates (a member of old military aristocracy). Subdued Micheal's Seljuk forces and in March 1078 he was crowned emperor after Michael renounced his throne.

1078-1081.

Did nothing. Good fighter couldn't lead the Byzantine empire. Problems got worse. Empire nearly collapsed.