Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question and for your concern to get your acts of worship accepted by Allah the Almighty.
As for your query, there are many sins that may cause man to be deprived of the reward of his good deeds such as unfaithfulness (shirk), ostentation (riya’), disobeying parents, etc.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states,
Shirk is one of the major sins that invalidates our actions. Allah Almighty says, “And yet, it has already been revealed to you [O man,] as well as to those who lived before thee, that if thou ever ascribe divine powers to aught but God, all thy works shall most certainly have been in vain: for [in the life to come] you shall most certainly be among the lost.” (Az-Zumar 39:65)
Next to shirk comes riya’ or ostentation which means doing good deeds for other than seeking the pleasure of Allah. Some scholars include it as a category of shirk. Allah Almighty says, “As for those who care for [no more than] the life of this world and its bounties -We shall repay them in full for all that they did in this [life], and they, shall not be deprived of their just due therein: [yet] it is they who, in the life to come, shall have nothing but the fire -for in vain shall be all that they wrought in this [world], and worthless all that they ever did !” (Hud 11:15)
Still another factor that deprives the rewards and blessings of good deeds is boastfulness and hurting the feelings of those whom we help through charities. Allah Almighty says, “O you who have attained to faith! Do not deprive your charitable deeds of all worth by stressing your own benevolence and hurting [the feelings of the needy], as does he who spends his wealth only to be seen and praised by men, and believes not in God and the Last Day: for his parable is that of a smooth rock with [a little] earth upon it – and then a rainstorm smites it and leaves it hard and bare. Such as these shall have no gain whatever from all their [good] works: for God does not guide people who refuse to acknowledge the truth.” (Al-Baqarah 2:264)
The above list is not exhaustive. For there are other grave sins which may also deprive us the rewards of our good deeds such as hurting one’s parents, victimizing people through aggression or depriving them of their rights, etc.
I pray to Allah to purge our hearts and actions of such heinous sins and accept our good deeds.
Allah Almighty knows best.