Centralized data storage systems face significant challenges regarding unauthorized tampering and a lack of verifiable audit trails. This paper presents BlockSecure, a web-based secure storage system that integrates AES-256 encryption with a custom C#-based blockchain engine. Built on ASP.NET Core MVC and MongoDB, the framework ensures data confidentiality through unique per-file encryption keys and provides immutability via a Proof-of-Work (PoW) consensus mechanism. SHA-256 hashes of encrypted files are anchored into a permanent ledger, enabling real-time detection of data tampering. Experimental results confirm that the proposed system delivers superior security and accountability compared to conventional cloud-based storage solutions.