Vishwamitra's penance was rendered void twice(Once broken , it needs to be started from beginning). Once by Menaka and the second time by Rambha.
In the First Case, Vishwamitra fell for Menaka's beauty and his lust overcame his desire for enlightenment. He spent 10 years with Menaka. Thereafter , he desired to do Penance again.
Then at a long lost time Menaka, the prominent apsara, celestial wench, has arrived and started to swim for sport in that holy lake. That great resplendent sage Vishvamitra has seen Menaka who is incomparable in her mien and comparable to an electric-flash in a black-cloud, while she is swimming in the holy lake. On seeing her the sage having gone under the sway of Love-god said this to her, 'oh, apsara, you are welcome, I invite you to bide in my hermitage. Oblige me who am bewitched by Love-god for you. You be safe.’
"When he said thus to her, oh, Raghava, then she made a stopover there and ten years rolled by comfortably, and oh, gentle Rama, because of her staying Vishvamitra is indeed faced with a great hindrance in his ascesis. Then after the lapse of that ten year period Vishvamitra became doleful with distress and he is enwrapped in humiliation, as it were, and, oh, Rama, Raghu's legatee, then a resentful thought occurred to him.
" 'All this is the mischief of gods to defraud me of the great merit of my ascesis. Ten years have rolled by as if they are just a day and a night. Furthermore, I who am under the influence of lust and lure had to encounter this hindrance in my ascesis.' Oh, Rama, that best saint suspired heavily when he became emotional with reparation. But on seeing the scared celestial wench Menaka, who is shivering and waiting with suppliantly adjoined palms, he sent her away with pleasant words, and he that Vishvamitra indeed went to the northern Himalayan mountain.
He started penance again. This time Indra send Rambha to disrupt his penance. Having understood intention of Rambha to Lure him again, Vishwamitra trembled in Wrath and Uttered a Curse transforming Rambha to stone. Because of his wrath, once again he Lost everything gained through Acsesis.
At the instance of Indra, that lovely nymph clad in enchanting raiment, faintly smiling, went forth to allure the heart of Shri Vishvamitra.
At that moment, the liquid notes of the cuckoo began to delight the rishi and he then beheld the nymph Rambha. Stirred by the cuckoo’s note and the ravishing sound of the beautiful Rambha’s song, Shri Vishvamitra, recollecting his former fall, was filled with misgiving and recognizing the design of the god Indra, transported with rage, cursed Rambha, saying:—
“O Rambha, O Unfortunate One, you have come hither to lure me from my penance, I, who have conquered lust and anger. Mayest you become petrified and take the form of a rock for ten thousand years. A brahmin perfected in the power of Yoga shall one day deliver you from this curse.”
Having pronounced this curse on Rambha, the rishi became a prey to remorse, for, giving way to wrath he lost the fruit of all his yogic practices.
In the Final try he succeeded and Became a Brahmarishi Conquering all His emotions and attachments to material items..